Apparatus for damping vibrations

ABSTRACT

Apparatus for damping vibrations between the output element of the engine and the power train in a motor vehicle has flywheels which are rotatable relative to each other. One flywheel is mounted on the output element of the engine and another flywheel is connectable to the power train by a friction clutch. Vibration dampers are installed between the flywheels, and such dampers are confined in a housing which is provided on the one flywheel and contains a supply of viscous fluid medium for the parts of the dampers. The housing is the input member of the dampers and the output member of the dampers is a flange which extends into the housing and is axially movably coupled to the other flywheel.

CROSS-REFERENCE TO RELATED CASES

This is a division of commonly owned U.S. patent application Ser. No.08/856,213 filed May 14, 1997, which is a division of Ser. No.08/320,732 filed Oct. 7, 1994 now abandoned, which is a division of Ser.No. 08/060,490 filed May 7, 1993 now U.S. Pat. No. 5,487,704, which is acontinuation of Ser. No. 07/626,384 filed Dec. 12, 1990, now abandoned,which is a continuation of Ser. No. 07/434,524 filed Nov. 7, 1989, nowabandoned, which is a continuation of Ser. No. 07/063,301 filed Jun. 17,1987, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to apparatus for damping vibrations, especiallytorsional vibrations between the output element (e.g., a crankshaft) ofan engine and the power train in a motor vehicle. More particularly, theinvention relates to improvements in apparatus of the type having atleast two flywheels which are rotatable relative to each other againstthe opposition of damper means wherein one flywheel is the input memberand the other flywheel is the output member of the damper means. Theoutput member can be coupled to the power train by a clutch,particularly a friction clutch.

Heretofore known vibration damping apparatus of the above outlined typeemploy dampers which have energy storing elements acting in thecircumferential direction of the flywheels and normally including coilsprings which store elastic energy, and additional energy storingelements which act in the axial direction of the flywheels and cooperatewith friction pads and/or linings to produce friction (i.e.,hysteresis). The means for generating friction operate in parallel withenergy storing means which act in the circumferential direction of theflywheels.

It has been found that certain conventional vibration damping apparatuscan operate satisfactorily (i.e., they are capable of damping torsionalvibrations as well as noise) but only under specific circumstances.Thus, the mode of operation of such conventional apparatus is notentirely satisfactory under many operating conditions because theirdesign is a compromise due to an attempt to ensure satisfactory oracceptable operation under a variety of different conditions. Forexample, a purely mechanical solution does not suffice to cover a widespectrum of operating conditions entailing the development of manybasically different stray movements and noise levels. Moreover, purelymechanical solutions are quite expensive, especially if they are toadequately suppress stray movements and noise under a variety ofdifferent operating conditions. This is due to the fact that, if amechanically operated vibration damping apparatus is to counteract awide range of amplitudes of undesirable stray movements of the flywheelsrelative to each other, such undertaking greatly increases the cost,bulk, complexity and sensitivity of the apparatus. Moreover, even a verycomplex and expensive mechanical vibration damping apparatus isincapable of operating satisfactorily under any one of a wide range ofdifferent operating conditions because the individual damper stages(i.e., hystereses produced by individual energy storing elements whichact in the circumferential direction of the flywheels) cannot be alteredas a function of changes in operating conditions. Still further,presently known apparatus are subject to extensive wear so that theiruseful life is relatively short, and they are also prone to malfunction.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invention is to provide a vibration and noise dampingapparatus whose versatility exceeds that of heretofore known apparatusand which can be used in a wide variety of systems for transmission oftorque, especially between the engines and power trains of motorvehicles.

Another object of the invention is to provide an apparatus whose dampingcharacteristics (i.e., the rate of energy dissipation) can conform tothe vibration and/or noise generating behavior of motor vehicles under awide variety of different operating conditions and/or other influences.

A further object of the invention is to provide an apparatus which canbe used to connect existing engines or other prime movers with existingpower trains.

An additional object of the invention is to provide an apparatus whichoperates properly at low or high rotational speeds as well as atresonance RPM and during starting or stoppage of the engine in a motorvehicle.

Still another object of the invention is to provide an apparatus whichcan properly prevent transmission of undesirable stray movements betweenan engine and a power train under a variety of apparently contradictoryor conflicting circumstances without affecting the quality, reliabilityand/or reproducibility of the vibration- and/or noise-suppressingaction.

Another object of the invention is to provide a relatively simple,compact and inexpensive apparatus which can be readily assembled ortaken apart and whose useful life is eminently satisfactory forutilization between the engines and power trains of motor vehicles ofall or nearly all kinds.

An additional object of the invention is to provide an apparatus whichcomprises a relatively small number of relatively simple and inexpensiveparts and wherein the percentage of components which need not undergosecondary treatment in material removing tools and the like is higherthan in heretofore known apparatus.

A further object of the invention is to provide an apparatus wherein thewear upon the parts which move relative to each other is not pronouncedand whose utilization entails minimal losses in the driving system.

Another object of the invention is to provide novel and improvedflywheels for use in the above outlined apparatus.

A further object of the invention is to provide a novel and improvedmethod of broadening the range of utility of apparatus for counteractingvibrations and the transmission of noise between the engines and powertrains of motor vehicles.

An additional object of the invention is to provide a motor vehiclewhich embodies the above outlined apparatus.

A further object of the invention is to provide the apparatus with noveland improved means for suppressing stray movements of several flywheelswhich are rotatable relative to each other and serve to transmit torquebetween a prime mover and a transmission or the like.

Still another object of the invention is to provide the apparatus withnovel and improved means for damping stray movements of severalflywheels with reference to each other.

A further object of the invention is to provide an apparatus which cangenerate a variety of damping actions, either simultaneously or duringselected stages of transmission of torque between a prime mover and apower train or the like.

An additional object of the invention is to provide an apparatus whereina highly satisfactory damping action can be generated by the mediumwhich is used to prolong the useful life of moving parts.

A further object of the invention is to provide the apparatus with noveland improved means for transmitting torque between its components insuch a way that the components can be readily separated, reassembled andinspected in a time-saving operation.

Another object of the invention is to provide the apparatus with noveland improved means for varying the vibration- and/or noise-dampingaction in automatic response to changes in operating conditions.

The invention is embodied in an apparatus for damping vibrations,especially between an engine and a power train. The apparatus comprisesa composite flywheel including a first flywheel which is connectablewith the engine (e.g., with a crankshaft which is driven by the engine)and a second flywheel which is connectable with the power train (e.g.,by way of a friction clutch which is installed between the secondflywheel and the input shaft of a change-speed transmission of the powertrain). The flywheels are rotatable relative to each other against theopposition of damper means which operates between the flywheels, thefirst flywheel constituting the input member and the second flywheelconstituting the output member of the damper means. One of the first andsecond flywheels includes or carries a housing which defines at leastone annular compartment having a substantially closed (e.g.,substantially circular) cross-sectional outline. The damper meansincludes at least one damper having a plurality of deformable energystoring elements (such as coil springs) which are installed in thecompartment, and the housing preferably closely conforms to the outlinesof the energy storing elements (i.e., the energy storing elements of theone damper are snugly received in the compartment). The one damperfurther comprises means for deforming the energy storing elements in thecompartment, and such deforming means includes first abutment meansprovided on the housing and located in the compartment and a deformingmember (hereinafter called flange for short) which is rotatable with theother of the first and second flywheels and has second abutment means inthe compartment. Still further, the damper means comprises a supply ofviscous fluid medium (such as a paste) which at least partially fillsthe compartment.

The flange and the housing can define a narrow gap which communicateswith the compartment, and the second abutment means preferably extendssubstantially radially of the one flywheel. The second abutment meanscan include radially outwardly extending arms which are integral partsof the flange and form an annulus in a plane making an angle of 90degrees with the axes of the flywheels. At least one of the arms caninclude an extension which is disposed in the compartment radiallyoutwardly of the adjacent energy storing element or elements and ispreferably received in a portion of the compartment so that its innerside is adjacent the radially outermost portion or portions of theadjacent energy storing element(s).

The housing can include two substantially shell-shaped parts or sectionsand at least one of these sections can consist of a deformable (ductile)metallic sheet material which can be shaped in a press or a likemachine. Each section can constitute a half shell.

The compartment is or can constitute a circumferentially completeannulus, and the first abutment means can constitute discrete stops inthe compartment. Such stops can be riveted, welded or otherwise fixedlysecured to the respective sections of the housing to alternate with thesecond abutment means (such as the aforementioned arms of the flange) inthe neutral position of the one damper.

At least those portions of the abutment means which actually contact theenergy storing elements can have a pronounced hardness. Such pronouncedhardness can be achieved as a result of thermal treatment of theaforementioned portions of the abutment means. Alternatively or inaddition to such thermal treatment, selected portions of the abutmentmeans and/or of the energy storing elements and/or of the sections ofthe housing can be provided with coatings of a material which exhibits apronounced hardness.

The first abutment means can be integral with the housing; for example,such integral first abutment means can include pockets which areprovided on one or both sections of the housing and extend into thecompartment.

The apparatus can comprise separately produced means for reducingfrictional engagement of the housing with the energy storing elements,and such means is preferably disposed radially outwardly of the energystoring elements in the compartment and can include at least one insertin the form of a strip or band of steel or the like. The insert orinserts are received in suitable recess(es) of the housing. For example,the entire frictional engagement reducing means can include a singlesteel band whose end portions are anchored in the housing and whosematerial exhibits a pronounced hardness.

The band can have a concave side which faces the energy storing elementsin the compartment and extends along an arc of 45-120 degrees,preferably along an arc of 60-90 degrees in the circumferentialdirection of the normally circular cross-sectional outline of thecompartment.

The apparatus can further comprise retainer means interposed between atleast one of the abutment means and the energy storing elements,particularly between the energy storing elements and the second abutmentmeans. Each retainer means can have an outline which closely conforms tothat of the surfaces forming part of the housing and bounding thecompartment. The energy storing elements are preferably springs (such ascoil springs) having hollow end portions and at least one of theretainer means has an extension in the end portion of the adjacentspring. Such extension can have a substantially conical shape to bereadily receivable in the end portion of the adjacent spring. Theconicity of the extension can be such that it automatically reenters theend portion of the adjacent spring upon each separation of such endportion from the extension in response to subsequent movement of the endportion of the spring toward the extension and/or vice versa. Eachretainer means can act not unlike a piston for the fluid medium in thecompartment, and at least one of the retainer means can define a pathfor the flow of fluid medium therethrough (e.g., through an opening orhole or notch or recess in the retainer means) substantially in thecircumferential direction of the flywheels.

The compartment can have a varying cross-sectional area in the region ofat least one energy storing element to influence the flow restrictingaction of the housing in such region and hence the damping action of thedamper as a result of different resistance to the flow of fluid medium.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved apparatus itself, however, both as to its construction and itsmode of operation, together with additional features and advantagesthereof, will be best understood upon perusal of the following detaileddescription of certain specific embodiments with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an axial sectional view of a vibration damping apparatus whichembodies one form of the invention and wherein the damper meanscomprises two dampers;

FIG. 2 is a fragmentary end elevational view as seen in the direction ofarrow II in FIG. 1;

FIG. 3 is a fragmentary axial sectional view. of a second apparatuswherein one section of the housing for the dampers serves to center theother section;

FIG. 4 is a fragmentary axial sectional view of a third apparatuswherein both sections of the housing are made of deformable metallicsheet material;

FIG. 5 is a fragmentary sectional view as seen in the direction ofarrows from the line V-V of FIG. 4;

FIG. 6 is an axial sectional view of a fourth apparatus with a differentsealing device between the flywheels radially inwardly of the innerdamper;

FIG. 6a is a is an enlarged view of the detail within the phantom-linecircle "X" of FIG. 6;

FIG. 7 is a fragmentary end elevational view of the fourth apparatus asseen in the direction of arrow VII in FIG. 6;

FIG. 7a illustrates the manner on anchoring the ends of a frictionalengagement reducing band in the housing of the apparatus which is shownin FIGS. 6, 6a and

FIG. 8 is a fragmentary axial sectional view of a fifth apparatuswherein the compartment for the outer damper is sealed from thecompartment for the inner damper in a different way.

FIG. 9 is a fragmentary axial sectional view of a sixth apparatuswherein the sections of the housing for the damper or dampers arecoupled to each other by ring-shaped cage;

FIG. 10 is an axial sectional view of a seventh apparatus wherein theinner and outer dampers are connected in series;

FIG. 11 is a fragmentary axial sectional view of an eighth apparatuswith a single damper;

FIG. 12 is a fragmentary sectional view as seen in the direction ofarrows from the line XII-XII of FIG. 11;

FIG. 13 is a fragmentary sectional view as seen in the direction ofarrows from the line XIII--XIII of FIG. 12;

FIG. 14 is a fragmentary axial sectional view of a ninth apparatus;

FIG. 15 is a fragmentary sectional view as seen in the direction ofarrows from the line XV--XV of FIG. 14;

FIG. 16 is a fragmentary sectional view of a tenth apparatus with anabutment which can be used in the apparatus shown in other Figures;

FIG. 17 is a fragmentary axial sectional view of an eleventh apparatuswherein the radially outermost portions of the housing sections areconfigurated in a different way;

FIG. 18 is a fragmentary axial sectional view of a twelfth apparatuswherein each section of the housing for the damper means has an innerlayer and an outer layer;

FIG. 19 is a fragmentary axial sectional view of a thirteenth apparatuswherein the damper means comprises a hydraulic damper and a dry frictiongenerating device;

FIG. 20 is a fragmentary axial sectional view of a fourteenth apparatuswherein the damper means comprises a hydraulic damper and a slip clutch;

FIG. 21 is a fragmentary axial sectional view of a fifteenth apparatuswith three concentric dampers disposed at different distances from theaxes of the flywheel; and

FIG. 22 is a fragmentary axial sectional view of a sixteenth apparatuswherein two dampers are disposed at the same distance from the axes ofthe flywheels.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The apparatus 1 which is shown in FIGS. 1 and 2 is used to damptorsional vibrations between the internal combustion engine and thepower train including a change-speed transmission of a motor vehicle.The apparatus 1 can be considered a unit of the power train andcomprises a composite flywheel 2 having a first component 3 and a secondcomponent 4. The components 3 and 4 (hereinafter called flywheels) arerotatable relative to each other and the flywheel 3 is non-rotatablyaffixed to the output element 5 (such as a crankshaft) of the engine byan annulus of bolts 6 or analogous fastener means. The flywheel 4 isconnectable to the input shaft 10 of a change-speed transmission inresponse to engagement of a friction clutch 7.

The friction clutch 7 comprises an axially movable pressure plate 8which is disposed between the flywheel 4 and a clutch cover 11 and isnon-rotatably but axially movably secured to the flywheel 4 and/or cover11 by a set of leaf springs (not shown) in the customary way. Adiaphragm spring 12 at the inner side of the cover 11 is tiltablebetween two annular seats and normally bears against the pressure plate8 to urge the latter toward the friction surface 70 of the flywheel 4whereby the friction surface 70 cooperates with the adjacent surface ofthe pressure plate 8 to clamp the friction linings at the periphery of aclutch plate or clutch disc 9 having a hub which is non-rotatablymounted on the input shaft 10 of the transmission. The means fordisengaging the clutch 7 can comprise an antifriction bearing which ismovable in the direction of arrow II in FIG. 1 in order to engage theradially inwardly extending prongs of the diaphragm spring 12 and tothereby tilt the spring so as to allow the pressure plate 8 to moveaxially and away from the flywheel 4.

The apparatus 1 further comprises damper means including a first orouter damper 13 and a second or inner damper 14. The dampers 13, 14 aredisposed between the flywheels 3, 4 and serve to oppose but to permitangular movements of the flywheel 3 relative to the flywheel 4 and/orvice versa. The damper 14 operates in parallel with the damper 13.

The means for rotatably mounting the flywheel 4 on the flywheel 3 orvice versa comprises antifriction bearing means 15 including anantifriction ball or roller bearing 16 having a single annulus ofrolling elements. The illustrated rolling elements are balls which aremounted between an outer race 17 and an inner race 19 of the bearing 16.The outer race 17 is installed in an axial recess 18 of the flywheel 4,and the inner race 19 surrounds an axial protuberance 20 which is anintegral part of the flywheel 3, which extends axially in a directionaway from the output element 5 of the engine, and which is received inthe recess 18 of the flywheel 4. The inner race 19 is a press fit on acylindrical peripheral surface or seat 20a of the protuberance 20 and isheld against axial movement relative to the flywheel 3 by an externalannular shoulder 21 of the protuberance 20 and a washer-like retainingring 22 which is secured to the end face of the protuberance 20 by a setof screws or other suitable fastener means.

The means for holding the outer race 17 of the bearing 16 against axialmovement relative to the flywheel 4 comprises two rings 23, 24 each ofwhich has a substantially L-shaped cross-sectional outline and whichextend into the recess 18. A disc 27 cooperates with the rings 23, 24 tohold the outer race 17 against axial movement relative to the flywheel4. The disc 27 can be considered an integral part of the flywheel 4; itis permanently (or more or less permanently) secured to the flywheel 4by rivets 26 or other suitable fastener means. The radially extendingportion 23a of the ring 23 abuts the adjacent side of the disc 27, andthe radially extending portion 24a of the ring 24 abuts a shoulder 25which is machined into or is otherwise formed in the recess 18. Thus,the outer race 17 is confined between the rings 23, 24 and these ringsare respectively flanked by the disc 27 and shoulder 25. The rings 23,24 together form a thermal insulator which prevents or reduces thetransfer of heat between the friction surface 70 of the flywheel 4 andthe bearing means 15. Each of these rings further includes an axiallyextending cylindrical portion which surrounds the adjacent part of theperipheral surface of the outer race 17. The portions 23a, 24a of therings 23, 24 preferably extend radially inwardly beyond the outer race17 so that they are adjacent the respective end faces of the inner race19. It is preferred to configurate and mount the radially extendingportions 23a, 24a of the rings 23, 24 in such a way that they actuallybear against (i.e., sealingly engage) the respective end faces of theinner race 19 so as to confine the lubricant (e.g., a suitable grease)for the rolling elements of the antifriction bearing 16. The sealingaction of the radially extending portions 23a, 24a can be enhanced byresilient elements 28, 29 (e.g., diaphragm springs) which are providedto urge the radially innermost parts of the portions 23a, 24a againstthe respective end faces of the inner race 19. The resilient element 28reacts against the disc 27 and bears against the radially innermost partof the radially extending portion 23a, and the resilient element 29reacts against the radially innermost portion of the flywheel 4 andbears against the radially innermost part of the radially extendingportion 24a.

The flywheel 3 constitutes or forms part of a housing defining anannular chamber 30 for the dampers 13 and 14. This flywheel comprisestwo substantially shell-shaped parts or sections 31, 32 having radiallyoutermost portions which are secured to each other by threaded fasteners33 in the form of screws or the like. These fasteners ensure that theinner side or surface 34 of the part 31 abuts the adjacent side orsurface 35 of the part 32. The sides 34, 35 of the parts 31, 32 of theflywheel 3 are located radially outwardly of the chamber 30 and of thedampers 13, 14 therein. The means for sealing the chamber 30 in theregion of the abutting sides 34, 35 of the parts 31, 32 comprises atleast one sealing ring 36 which is recessed into the side 34 and/or 35and is deformed in response to the application of fasteners 33. Suchfasteners are disposed radially outwardly of the sealing ring 36. In theembodiment of FIGS. 1 and 2, the sealing ring 36 is recessed into agroove 37 in the side 34 of the part 31. In order to ensure accuratepositioning of the parts 31, 32 relative to each other during assemblyof the apparatus 1, these parts are provided with registering axiallyparallel bores or holes which are disposed radially outwardly of thesealing ring 36 and receive centering pins 38.

The radially outermost portion of the part 31 of the flywheel 3 isformed with a circumferentially extending cylindrical surface 39 whichis surrounded by a ring-shaped starter gear 40. The parts 31, 32 of theflywheel 3 can be made of cast iron. However, if it is desirable toreduce the inertia of the flywheel 3, at least one of the parts 31, 32(particularly the part 31) can be made of a light metal alloy,particularly a casting of aluminum alloy. An advantage of such castlightweight parts is that they can be mass-produced in accordance with acompression, molding, stamping or like technique and require a minimumof secondary treatment.

The axial position of the gear 40 can be selected by causing such gearto abut the tips of the fasteners 33, i.e., the fasteners can serve as ameans for locating the gear 40 in a predetermined axial position withreference to the flywheel 3.

The dampers 13, 14 comprise a common output member in the form of aradial flange 41 which is disposed axially between the parts 31, 32 ofthe flywheel 3. As shown in FIG. 2, the radially innermost portion ofthe flange 41 is non-rotatably but axially movably connected to the disc27 by a torque transmitting connection 42. The disc 27 is secured to theflywheel 4, and more specifically to the end face of the axiallyextending projection 43 of the flywheel 4 by means of the aforementionedrivets 26. The projection 43 extends toward the output element 5 of theengine. In order to facilitate and ensure accurate centering of the disc27 on the projection 43 during assembly of the apparatus 1, theprojection 43 is or can be provided with a centering seat 43a for thedisc 27.

The flange 41 comprises radially outwardly extending abutments or arms44 which alternate with energy storing elements 45 of the outer damper13. Each such energy storing element 45 constitutes an arcuate coilspring. The arms 44 alternate with recesses 46 for the respective coilsprings 45, and each such recess is disposed radially outwardly of oneof three arcuate windows 47 for energy storing elements 48 (preferablycoil springs) of the inner damper 14. The flange 41 further comprisesarcuate webs or ribs 49 which extend in the circumferential direction ofthe flywheel 3 between the recesses 46 and the windows 47. The ribs 49connect the neighboring arms 44 to each other and which also connect toeach other radially extending partitions or webs 50 which are providedbetween neighboring windows 47 of the flange 41. The coil springs 45 ofthe outer damper 13 can bear against the arms 44, and the coil springs48 of the inner damper 14 can bear against the radially extending webs50. The ribs 49 and webs 50 together form a ring between the dampers 13and 14.

The radially outermost portion of the chamber 30 has a substantiallycircular cross-sectional outline and forms a compartment 51 for the arms44 of the flange 41 as well as for the coil springs 45 of the outerdamper 13. The compartment 51 is formed primarily by arcuate grooves 52,53 which are mirror symmetrical to each other and are respectivelyprovided in the sides or surfaces 34, 35 of the parts 31, 32. Thegrooves 52, 53 flank the radially outermost portion (including the arms44) of the flange 41 and each thereof receives a little less thanone-half of each coil spring 45. The radially innermost portion of thecompartment 51 of the chamber 30 is substantially sealed by the ribs 49of the flange 41 save for a relatively narrow radially extendingclearance or gap 54 at one side of the flange 41. The compartment has acircular cross-sectional outline which is complete (closed) save at thelocation of entry of the flange 41.

As shown in FIG. 1, the configuration of the grooves 52, 53 in the parts31, 32 of the flywheel 3 is selected in such a way that thecorresponding portions of the coil springs 45 are received therein witha minimum of play. The surfaces bounding the radially outermost portionsof the grooves 52 and 53 can serve to guide and confine the adjacentradially outermost portions of the convolutions of coil springs 45 inthe compartment 51 of the chamber 30. The arrangement is such that theradially outermost portions of the convolutions of coil springs 45 abutor can abut the surfaces bounding the adjacent radially outermostportions of the grooves 52 and 53, at least when the composite flywheel2 rotates and the coil springs 45 are acted upon by centrifugal force. Areasonably large surface-to-surface contact between the convolutions ofthe coil springs 45 and the parts 31, 32 of the flywheel 3 is oftendesirable in order to achieve a substantial reduction of wear and, morespecifically, to distribute the wear over larger portions of theconvolutions and surfaces bounding the grooves 52, 53 in the radiallyoutermost portion of the compartment 51.

The end convolutions of the coil springs 45 bear against abutments orstops 55, 55a which are provided in the compartment 51 so that theyextend into the grooves 52, 53 and flank the adjacent radially outwardlyextending arms 44 of the flange 41. As shown in FIG. 2, the abutments 55and 55a can be oriented in the same way as the adjacent arms 44, i.e.,substantially radially of the flywheel 3. The abutments 55, 55a havesubstantially mirror symmetrical parts 56, 57 which are respectivelyreceived in the grooves 52, 53 and are affixed to the correspondingparts 31, 32 of the flywheel 3 by rivets 58 or in any other suitableway. Portions of the abutments 55, 55a are preferably flattened toensure a more satisfactory engagement with the respective coil springs45. Each arm 44 is located between two abutments 55, 55a as seen in theaxial direction of the apparatus 1.

Cup-shaped spring retainers 59 are provided at the circumferential endsof the arms 44 (see FIG. 2). The cross-sectional area of each retainer59 matches or approximates the cross-sectional area of the compartment51. Each retainer 59 is located between an arm 44 and one end of therespective coil spring 45.

The sides or surfaces 34, 35 of the parts 31, 32 includecircumferentially complete ring-shaped portions 60, 61 which aredisposed radially inwardly of the compartment 51 and flank a ring-shapedpassage 62 for the corresponding portion of the flange 41. The width ofthe passage 62 (as measured in the axial direction of the flywheel 3)slightly exceeds the thickness of the corresponding portion of theflange 41 (namely the thickness of the portion between the portions 60,61 of the sides or surfaces 34, 35) so that the flange 41 and at leastone of the parts 31, 32 define the afore-mentioned gap 54. The width ofthe gap 54 can be 0.1-2 mm.

The surface portions 60, 61 which flank the ring-shaped passage 62 aredisposed radially outwardly of a second compartment which includesarcuate grooves 63, 64 machined into or otherwise formed in the parts31, 32 and serving to receive portions of the coil springs 48 which formpart of the inner damper 14. The diameters of convolutions of the coilsprings 48 are such that each such convolution extends axially beyondboth sides of the adjacent portion of the flange 41.

FIG. 1 shows that at least the radially outermost portions of thegrooves 63, 64 are bounded by surfaces which are complementary to thesurfaces of adjacent coil springs 48 so that the coil springs 48 are atleast partially guided and confined by such surfaces, at least in theaxial direction of the apparatus 1. Each of the grooves 63, 64preferably extends through an angle of 360 degrees, the same as thegrooves 52, 53 which form part of the compartment 51 for the coilsprings 45. This is of advantage because the grooves 52, 53, 63 and 64can be formed during casting of the parts 31, 32 and can be finished byturning or in accordance with another suitable material removingtechnique. The means for stressing the coil springs 48 (i.e., forstressing the energy storing elements of the inner damper 14) comprisesabutments or stops 65, 66 which are installed in the grooves 63, 64 andare preferably provided with flattened portions in contact with thehollow ends of the coil springs 48. Thus, the configuration of each ofthe abutments 65, 66 preferably conforms to that of the adjacent portionof the surface bounding the respective groove 63, 64, and theseabutments are affixed to the respective parts 31, 32 of the flywheel 3by rivets 67. FIG. 2 shows that the abutments 65, 66 (which are disposedat opposite sides of the radially extending webs 50 of the flange 41, asseen in the axial direction of the apparatus l) are shorter than thecorresponding webs 50 (as seen in the circumferential direction of theflywheel 3).

The dimensions of the ribs 49 of the flange 41 are selected (withreference to the grooves 63, 64) in such a way that the coil springs 48abut the ribs 49, at least when the flywheel 3 rotates and the coilsprings 48 are acted upon by centrifugal force. This does not entail anexcessive amount of wear, especially if the flange 41 is made of steelwhich is hardened at least along its surface to thus reduce wear uponthose portions which are disposed radially and are engaged by the coilsprings 48. Another advantage of the feature that the ends of the coilsprings 48 bear radially against the webs 49 is that the coil 'springs48 can be twisted or turned with the flange 41 before they engage theabutments 65, 66 and this does not result in the development ofexcessive friction with the parts 31, 32 of the flywheel 3 under theaction of centrifugal force. Such friction is often undesirable becauseit can distort the characteristics of the outer damper 13.

FIG. 2 shows that the apparatus 1 comprises three coil springs 45 andthree coil springs 48. Each outer coil spring 45 extends along an arc ofclose to or exactly 110 degrees, and the arcs formed by the inner coilsprings 48 preferably equal or approximate the arcs covered by the outercoil springs 45. In the embodiment of FIGS. 1 and 2, each inner coilspring 48 extends along an arc of approximately or exactly 100 degrees.Thus, the three outer coil springs 45 jointly extend along an arc whichapproximates 91 percent of a complete circle, and the three inner coilsprings 48 jointly extend along an arc which approximates 83 percent ofa complete circle.

The coil springs 45 and/or 48 are or can be straight prior tointroduction into the respective compartments of the flywheel 3. If thecoil springs are originally straight, they must be deformed duringinsertion into the chamber 30. However, it is equally within the purviewof the invention to make the coil springs 45 and/or 48 in such a waythat their curvature matches or approximates that of the respectivecompartments in the flywheel 3 before the springs are installed in thechamber 30. The utilization of "prefabricated" coil springs whosecurvature matches or approximates that of the grooves 52, 53 and 63, 64is preferred for convenience of assembly as well as to reduce internalstresses which develop during compression. Moreover, the prefabricatedcoil springs (i.e., springs whose curvature matches or approximates thecurvature of the compartment 51 and grooves 63, 64 prior to installationof the springs in the housing of the flywheel 3) are devoid of bendingmoments in neutral positions of the flywheels.

The chamber 30 contains a supply of a viscous fluid medium which is alubricant. For example, the chamber 30 can be partially filled withsilicon oil or grease. The quantity of viscous fluid medium ispreferably selected in such a way that, when the apparatus 1 is idle(i.e., when the flywheels 3 and 4 do not rotate), the upper level of thesupply of fluid medium extends at least to the level of the axis of thelowermost outer coil spring 45 so as to ensure that such spring will dipinto the supply of lubricant. It is presently preferred to select theupper level of the fluid medium in such a way that the lowermost innercoil spring 48 dips into the fluid medium, at least at the lowermostpoint of its axis and at the very least to such an extent that at leasta portion of one or more lowermost convolutions of the lowermost coilspring 48 dips into the supply of lubricant. This ensures thedevelopment of an adequate film of lubricant between the lowermostconvolutions of the lowermost spring 48 and the adjacent surfaces,particularly the surfaces of the respective web or webs 49, withattendant reduction of wear upon such surfaces. It is assumed that theaxis of the apparatus 1 which is shown in FIGS. 1 and 2 is horizontaland that the supply of fluid medium in the chamber 30 extends to thelevel of the lowermost portion of the axis of the lowermost coil spring48.

An advantage of the feature that the chamber 30 is provided in theflywheel 3, which is connected with the output element 5 of the engine,is that the chamber 30 is as remote from the flywheel 4 and from thefriction clutch 7 as possible, i.e., that the supply of fluid medium inthe chamber 30 is less likely to be affected by heat which is generatedat the friction surface 70 of the flywheel 4 when the clutch 7 is beingengaged or disengaged.

The apparatus 1 further comprises means for ventilating the region ofthe chamber 30 in the flywheel 3. Such ventilating means includes aradially extending annular channel 68 which is provided between the part32 and the flywheel 3 and the radially innermost portion of whichcommunicates with passages 69 provided in the flywheel 4 radiallyinwardly of the friction surface 70. The radially outermost portion ofthe channel 68 is open to the surrounding atmosphere.

As can be seen in FIG. 2, the flange 41 has a centrally located opening71 bounded by a surface which is provided with radially inwardlyextending tooth-like projections 72 mating with complementary tooth-likeprojections 73 at the periphery of the disc 27. The projections 72 and73 together constitute the aforementioned connection 42 which ensuresthat the flange 41 shares all angular movements of the disc 27 but thatthe flange 41 can find an optimum axial position between the parts 31,32 of the flywheel 3. This renders it possible to ensure that the widthof the aforementioned clearance 54 between the part 32 and the flange 41in the passage 62 can be very narrow or extremely narrow. Moreover, theconnection 42 including the projections 72 and 73 renders it possible toreadily compensate for eventual manufacturing tolerances of the partswhose surfaces are adjacent the flange 41.

The means for sealing the chamber 30 further comprises a sealing device74 which is installed between the disc 27 and the adjacent radiallyinnermost portion of the part 32. The sealing device 74 comprises asubstantially washer-like sealing member 75 having an inner portionwhich engages a shoulder 76 on the aforementioned projection 43 of theflywheel 4. A radially outer or outermost portion of the sealing member75 bears against the adjacent ring-shaped surface 77 of the radiallyinnermost portion of the part 32. The sealing member 75 can undergoaxial deformation not unlike a diaphragm spring. A diaphragm spring 78is provided to bias the sealing member 75 axially against the shoulder76 as well as against the surface 77. The spring 78 is installed inprestressed condition between the sealing member 75 and the flange 41.This spring further serves to bias the flange 41 axially toward thesurface portion 60 so that the gap 54 develops only between the flange41 and the surface portion 61. This gap communicates with thecompartment 51 and with those portions of the chamber 30 which arelocated radially inwardly of the compartment 51. FIG. 1 shows that thedevice 74 seals the annular chamber 30 from the aforementioned channel68 of the ventilating means for the housing (flywheel 3) of the chamber30. The inner diameter of the sealing member 75 exceeds the outerdiameter of the annulus of tooth-shaped projections 73 on the disc 27i.e., of the connection 42.

The provision of the torque transmitting connection 42 and sealng device74 renders it possible to simplify the assembly of the apparatus 1.Thus, the flywheels 3 and 4 are assembled with certain parts in a firststep, and the thus assembled flywheels are thereupon fixed in optimumaxial positions relative to each other by fastening the retaining ring22 to the protuberance 20 of the flywheel 3. The sealing device 74 ismounted on the flywheel 3 prior to assembly of the flywheels with eachother and the bearing means 15 is or can be form-lockingly mounted inthe recess 18 of the flywheel 4 before the recess 18 receives theprotuberance 20 of the flywheel 3. When the flywheel 4 is beingassembled with the flywheel 3, the inner race 19 of the antifrictionbearing 16 is slipped onto the protuberance 20 so that the internalsurface of the race 19 surrounds the cylindrical external surface 20a ofthe protuberance 20. The projections 73 are brought into mesh with thecomplementary projections 72 and, as the flywheels 3 and 4 are beingassembled, the radially innermost portion of the sealing member 75forming part of the sealing device 74 comes into abutment with theshoulder 76 so that the sealing member 75 is deformed (distorted) by thediaphragm spring 78 and bears against the shoulder 76. The final axialfixing of the flywheels 3 and 4 relative to each other involvesattachment of the retaining ring 22 to the protuberance 20 of theflywheel 3.

The utilization of torque transmitting connection 42 between theflywheels 3 and 4 is particularly desirable and advantageous when thehousing 31+32 forms an integral or detachable part of the flywheel 3,i.e., of that flywheel which is connectable to the output element 5 ofthe engine, and when the sealing device 74 is constructed and assembledin the aforedescribed manner so that the sealing member 75 is axiallystressed directly between the flywheels 3, 4 or between elements whichare integral with or attached to the two flywheels. The connection 42renders it possible to preassemble the apparatus 1 into two units orsubassemblies each of which includes one of the flywheels 3, 4 and tothereupon connect the subassemblies to each other by slipping the innerrace 19 of the bearing 16 onto the seat 20a of the protuberance 20 ofthe flywheel 3 prior to attachment of the retaining ring 22 to the endface of the protuberance 20. As shown in FIG. 1, the bolts 6 whichsecure the flywheel 3 to the output element 5 of the engine can alsoserve as a means for attaching the retaining ring 22 to the protuberance20.

The aforediscussed mounting of the flange 41 between the parts orsections 31, 32 of the housing for the chamber 30 in such a way that theflange has a certain freedom of axial movement against the opposition ofthe diaphragm spring 78 in the sealing device 74 is desirable andadvantageous on the additional ground that the flange 41 can find foritself an optimum orientation between the parts 31, 32 without undulystressing the adjoining elements of the apparatus. Moreover, suchmounting of the flange 41 ensures that the apparatus cannot generate apronounced frictional hysteresis in response to small angulardisplacements of the flywheels 3, 4 relative to each other when theengine of the motor vehicle is idling and/or under certain othercircumstances when the development of pronounced hysteresis is notdesirable.

In order to reduce wear upon the convolutions of the coil springs 45, 48and upon the adjacent portions of surfaces bounding the respectivegrooves 52, 53 and 63, 64, it is often desirable and advantageous toharden the corresponding portions of the parts 31 and 32. Such hardeningcan involve any suitable surface hardening procedure. Certain presentlypreferred treatments include induction hardening, case hardening,hardening with laser beams or flame hardening. If the wear upon thesurfaces which are adjacent the coil springs 45 and 48 is expected to beor is indeed very pronounced, it is advisable to coat the correspondingportions of the parts 31, 32 with layers of highly wear-resistantmaterial. Such layers can be applied to the surfaces bounding the entiregrooves 52, 53 and 63, 64 or to selected portions of such surfaces,e.g., in regions where the wear as a result of rubbing contact with thecoil springs 45, 48 is expected to be very pronounced. For example, thesurfaces bounding the grooves 52, 53 and/or 63, 64 can be chemicallycoated with layers of chromium, nickel, monybdenum or a plastic orceramic substance. The layers preferably consist of or contain amaterial which reduces the coefficient of friction between theconvolutions of the coil springs and the housing 31+32 to a minimum. Theapplied layers of such material can undergo a secondary treatment,particularly a polishing or other smoothing treatment, in order toenhance the quality of the surfaces in the regions of rubbing contactwith the coil springs. The secondary treatment can be carried out in agrinding, a milling or a like machine.

The recesses 46 in the flange 41 preferably extend along circular arcsof at least 45 degrees, more preferably 65-115 degrees and mostpreferably 80-100 degrees. When the flywheels 3 and 4 assume their idleor neutral positions, the coil springs 45 jointly extend along acircular arc which is between 70 and 96 percent of a complete circle. Asmentioned above, the coil springs 45 are or can be prefabricated in sucha way that their curvature matches or at least approximates thecurvature of the recesses 46 and ribs 49.

Angular displacement of the flywheels 3 relative to the flywheel 4and/or vice versa through a relatively large angle is desirable andadvantageous in most instances because the resistance to such angulardisplacement increases rather gradually, at least during the initialstage or stages of angular displacement, which is desirable for thedamping of large torsional vibrations and/or abrupt changes in angularvelocity of one of the flywheels relative to the other flywheel.Furthermore, this enables the viscous fluid medium in the chamber 30 todissipate large quantities of energy, i.e., to produce a pronouncedhysteresis.

However, the fluid medium is equally capable of damping angulardisplacements of small amplitude which require small hystereses anddevelop during operation under load. This is believed to be attributableto the fact that the pressure which develops in the fluid medium dependson momentary speed at which a certain volume of the fluid medium isbeing displaced. Thus, the damping capacity of the fluid medium (whichfills at least the compartment 51 of the channel 30) depends on thenature (extent and velocity) of angular displacement of the flywheelsrelative to each other. This renders it possible to achieve asubstantially automatic regulation of the damping action.

Each of the sections 31, 32 of the housing for the chamber 30 caninclude an inner layer which defines the compartment 51 and thecompartment including the grooves 63, 64, and an outer layer whichsurrounds the inner layer. A somewhat similar apparatus (1101) is shownin FIG. 18. It is also possible to provide inner and outer layers in theregion of the compartment 51 alone, or only in the region of thecompartment which includes the grooves 63, 64 for the energy storingelements 48 of the inner damper 48. The inner layers can be made of ahighly wear-resistant material which contains or consists of nickel,chromium, molybdenum of a suitable synthetic plattic substance.

The number of recesses for the coil springs of the outer damper and thenumber of windows for the coil springs of the inner damper need notexceed four. This ensures that each coil spring is relatively long andallows for a large annular displacement of the flywheels 3 and 4relative to each other.

The apparatus 1 of FIGS. 1 and 2 operates as follows:

When the flywheel 4 is caused to turn relative to the flywheel 3 fromthe illustrated idle position, the flange 41 is compelled to rotate withthe disc 27 by way of the connection 42 whereby the outer coil springs45 are compressed between the abutments 55, 55a and the arms 44 andstore energy. After the flywheel 4 has covered the angle 79 (see FIG.2), in one direction or the angle 80 in the opposite direction, theabutments 65, 66 reach the adjacent coil springs 48 so that, if theflywheel 4 continues to turn relative to the flywheel 3, the coilsprings 48 also begin to store energy. It goes without saying that thesituation is analogous if the flywheel 3 turns relative to the flywheel4 or if both flywheels turn but in opposite directions. The coil springs45 and 48 continue to store energy at the same time until thecompression of the inner coil springs 48 is completed, i.e., when eachof the springs 48 resembles, or acts not unlike, a solid block whichcannot undergo additional shortening in the circumferential direction ofthe flywheels. This terminates the angular movement of the flywheel 4relative to the flywheel 3. In the embodiment of FIGS. 1 and 2 (andstarting from the idle position of FIG. 2), the flywheel 4 can turn withreference to the flywheel 3 through an angle of 47 degrees in eitherdirection. The coil springs 45 rub against the surfaces surrounding thegrooves 52, 53 of the housing (flywheel 3) for the chamber 30 when theflywheel 4 turns relative to the flywheel 3 and/or vice versa so thatthe springs 45 cooperate with the parts 31, 32 to produce a frictionaldamping action. Additional friction is generated as a result of rubbingcontact between the flange 41 and the portion 60 of the surface 34 onthe part 31 under the bias of the diaphragm spring 78. Still further,frictional damping action develops as a result of sliding contactbetween the inner coil springs 48 and the adjacent surfaces bounding thegrooves 63 and 64 of the parts 31, 32, respectively.

The frictionally induced damping action between the coil springs 45, 48on the one hand and the surfaces bounding the grooves 52, 53 and 63, 64on the other hand varies as a function of changes of rotational speed.Thus, the frictionally induced damping action increases in response toincreasing RPM of the flywheels 3, 4 because the coil springs 45, 48 areacted upon by centrifugal force which urges their convolutions againstthe outer portions of surfaces bounding the respective grooves 52, 53and 63, 64.

Additional damping action is generated as a result of turbulence in anddisplacement of viscous fluid medium in the chamber 30. The body ofviscous fluid medium in the compartment 51 produces a more pronounced(hydraulic or viscous) damping action because the compartment 51 ispractically sealed from the remainder of the chamber 30 and thecup-shaped spring retainers 59 act not unlike pistons which slide in thearcuate cylinder-like compartment 51 of the chamber 30. When the outercoil springs 45 undergo compression, the cup-shaped retainers 59 sharethe movements of the respective arms 44 toward the correspondingabutments 55, 55a (such abutments also carry, or they can also carry,cup-shaped retainers) so that the viscous fluid medium which is confinedin the compartment 51 can escape (in response an abrupt change of theangular positions of flywheels 3, 4 relative to each other) only by wayof the very narrow clearance or gap 54 which connects the compartment 51with other portions of the chamber 30 radially inwardly of the springs45. The retainers 59 expel primarily viscous fluid which has filled thecoil springs 45 prior to compression of such springs as a result ofangular displacement of the flywheel 4 relative to the flywheel 3 and/orvice versa. The surfaces bounding the gap 54 act not unlike a flowrestrictor. Some fluid medium is also forced to pass or leak between thecup-shaped retainers 59 and the surfaces surrounding the compartment 51.The fluid medium which has been expelled from the compartment 51radially inwardly is redistributed uniformly in the radially outermostportion of the chamber 30 under the action of centrifugal force.

When the springs 45 are allowed to dissipate energy, some viscous fluidmedium in the compartment 51 is again caused to leak between thecup-shaped retainers 59 and the adjacent surfaces bounding the grooves52, 53 and flows through the gap 54 prior to returning into the radiallyoutermost portion of the chamber 30 under the action of centrifugalforce to fill the compartment 51 so that the springs 45 are fullyembedded in the fluid medium. The damping action of the fluid medium isa function of the centrifugal force, i.e., such damping action becomesmore pronounced when the RPM of the flywheels 3 and 4 increases.

The inner coil springs 48 dip into the supply of viscous fluid medium inthe chamber 30, at least in part, to thereby generate turbulence which,in turn, produces a hydraulic or viscous damping action.

The damping action of viscous fluid medium can be altered within a widerange by the expedient of providing one or more cup-shaped retainers 59with axially extending channels, recesses, grooves or holes and/or bythe expedient of altering the width of the gap 54. This renders itpossible to conform the damping action to requirements in a particularpower train. Additional regulation of the damping action which isfurnished by the viscous fluid medium can be achieved by removing one ormore retainers 59, i.e., by providing cup-shaped retainers only forselected coil springs. It is further possible to provide cup-shapedretainers for one or both ends of one or more inner coil springs 48 andone or more webs 50 of the flange 41. This renders it possible to carryout additional adjustments of the damping action which is furnished bythe fluid medium in the chamber 30.

The abutments 55, 55a, 65 and 66 (and/or the cup-shaped retainers 59)can be used as a means for determining and regulating the rate of fluidflow in the respective compartment(s) during certain stages of angularmovement of the flywheels 3 and 4 relative to each other to thus ensurethe establishment of a predetermined characteristic progress of dampingaction in dependency on certain operating parameters. Additionalregulation can be achieved by appropriate selection of constrictionsand/or enlargements in the housing including the parts or sections 31and 32, i.e., such housing can be configurated in such a way that thecompartment 51 and/or the compartment 63+64 includes portions ofconstant cross-sectional area and portions of varying cross-sectionalarea. This will be described in greater detail with reference to FIG. 7.

An advantage of the feature that the coil springs 45 and 48 practicallyfill the respective compartments 51 and 63+64 is that the surfacesbounding these compartments provide a highly satisfactory guidance forthe respective coil springs so that each of the dampers 13, 14 canemploy very long coil springs. Relatively long coil springs 45 and 48allow for larger angular displacements of the flywheels 3 and 4 relativeto each other. Furthermore, relatively long coil springs which undergoextensive compression and thereupon expand extensively back to theiroriginal length agitate and generate pronounced turbulence in the supplyof viscous fluid medium. The turbulence is also generated by the arms 44and webs 50 of the flange 41 and by the abutments 55, 56 and 65, 66 onthe housing parts or sections 31, 32. The hydraulic or viscous dampingaction which is generated in the just outlined manner varies as afunction of the amplitude and frequency of angular displacement of theflywheel 4 relative to the flywheel 3 and/or vice versa and also as afunction of the abruptness of such relative movements i.e., as afunction of the angular velocity and acceleration. The damping actionwhich is caused by the viscous fluid medium in the chamber 30 is also afunction of the RPM of the engine, i.e., this damping action can bevaried in dependency on a number of parameters including the angularvelocity of movement of the flywheels relative to each other, theacceleration of the flywheels relative to each other and the angularvelocity of the composite flywheel 2; each of these parameters can alterthe damping characteristics and hysteresis of the apparatus 1.

An advantage of the ribs 49 is that they guide the radially innermostportions of the coil springs 45 in the compartment 45 and the radiallyoutermost portions of coil springs 48 in the compartment including thegrooves 63 and 64 of the housing 31+32. The radially outermost portionsof the coil springs 48 bear against and are guided by the ribs 49 whilethey undergo compression or expansion and they merely bear against theribs 49 when they are not in the process of storing or dissipatingenergy. The ribs 49 serve a useful purpose also during the intervalswhen the coil springs 48 do not undergo compression, i.e., while thewebs 50 of the flange 41 move relative to the coil spring 48 and/or viceversa. Furthermore, all of the coil springs 48 need not be expanded orcompressed at the same time (this will be explained with reference toFIGS. 6 and 7), i.e., such coil springs can be grouped to operate duringdifferent stages of angular movement of the flywheels 3 and 4 relativeto each other. There is no relative sliding movement between theconvolutions of the coil springs 48 and the ribs 49 while the coilsprings 48 merely rotate with the flange 41. Thus, no frictional dampingaction is generated by the flange 41 and coil springs 48 during the justdiscussed stage or stages of operation of the apparatus 1.

As shown in FIG. 1, the two sections or parts 31, 32 of the housing forthe chamber 30 constitute the entire flywheel 3. However, and as shownfor example in FIG. 4, the flywheel 3 can include the sections or partsof the housing plus one or more additional parts.

The abutments 55, 55a, 65 and 66 can constitute plates, blocks or headsof rivets whose shanks are anchored in the respective parts 31, 32 ofthe housing for the chamber 30. Furthermore, the abutments 55, 55a, 65and/or 66 can be welded to the respective parts of the housing. Asmentioned above, wear upon the abutments and on the arms 44, ribs 49 andwebs 50 of the flange 41 can be reduced considerably if at least themost affected portions of the surfaces of such elements are surfacehardened or coated with layers of hard wear-resistant material.Chromium, molybdenum, nickel and certain plastic substances arepresently preferred coating materials. Moreover, it is possible to usecertain ceramic materials which can be treated to a high degree offinish and can stand long periods of use without extensive wear.

As a rule, or at least in many instances, the frictional and/orhydraulic damping action of the inner damper 14 is much less pronouncedthan that of the outer damper 13 which is in parallel with the damper14. This can be achieved by providing cup-shaped and/or otherwiseconfigurated spring retainers only in the compartment 51 and/or bydesigning the retainers for the coil springs 45 in such a way that theyfit more snugly in the compartment 51 than the retainers which arereceived in the compartment including the grooves 63, 64 for the coilsprings 48. In other words, the displacement of fluid medium in theouter compartment should be more pronounced than the displacement offluid medium in the inner compartment and the flow restrictor means forthe fluid in the outer compartment should produce a throttling actionwhich is more pronounced than the throttling action of flow restrictormeans in the inner compartment. If the coil springs of the inner damper14 are assembled into several groups, only one of these groups can beprovided with retainers so that the throttling action varies in responseto progressing angular displacement of the flywheels relative to eachother. Moreover, the coil springs 48 or at least some of the coilsprings 48 can be received in the housing 31+32 with a play whichexceeds the play between the coil springs 45 and the parts or sections31, 32. As mentioned above, the damping action can also be influenced byappropriate selection of the quantity of fluid medium in the chamber 30,e.g., in such a way that the compartment 51 is invariably filled whenthe flywheels 3, 4 rotate but the compartment for the coil springs 48 isfilled only in part. This ensures that the damping action of the damper13 is very pronounced in immediate response to start of angulardisplacement of at least one flywheel with reference to the otherflywheel. The damping action of coil springs 48 (which are normally onlypartly immersed in the fluid medium) is less pronounced (in fact, it canbe much less pronounced than that of the coil springs 45).

The apparatus of FIGS. 1 and 2 can be modified in the following way: Thesurfaces 60, 61 bounding the passage 62 and/or the adjacent surfaces ofthe flange 41 (including the surfaces of the ribs 49) can include orconstitute ramps which extend in the circumferential direction of theflywheel 3 and are designed to alter the effective area of the gap 54 inresponse to angular displacement of the flywheel 3 and/or 4 from itsneutral position with reference to the other flywheel, preferably insuch a way that the effective area of the gap 54 decreases withincreasing angular displacement from the neutral position. In otherwords, the flow restrictor including the flange 41 and the adjacentparts 31, 32 of the housing for the chamber 30 become more effectivewith increasing angular displacement of one of the flywheels withreference to the other flywheel. The aforementioned ramp or ramps can beprovided at one side, at the other side or at both sides of the flange41 and the height of such ramp or ramps varies in the axial direction ofthe flywheels 3 and 4.

FIG. 3 shows a portion of a second apparatus 101 wherein the part 132 ofthe flywheel 3 is made of a deformable metallic sheet material andincludes a cylindrical portion 132a which surrounds the part 131. Thepart 132 is adjacent but spaced apart from the flywheel 4. The internalsurface 135 of the portion 132a is adjacent the peripheral surface 134of the part 131; the surface 134 serves as a means for centering thepart 132 with reference to the part 131 and flywheel 4. A sealing ring136 (e.g., an O-ring) is recessed into a groove 137 in the surface 134of the part 131 to seal the radially outermost portion of the chamber130 from the atmosphere. A radially extending shoulder 135a of the part132 is located radially outwardly of the compartment for the coilsprings 45 and abuts a portion of the radially extending side or surface134a of the part 131. The shoulder 135a is closely or immediatelyadjacent the internal surface 135.

The means for holding the parts 131, 132 of the flywheel 3 against axialmovement away from each other comprises radially extending centeringmembers or pins 138 in holes which extend transversely of the surfaces134, 135. The pins 138. are preferably so-called heavy type dowel pinsand their outer end portions are surrounded by the starter gear 140.Each of these pins extends radially across the portion 132a of the part132 and into the radially outermost portion of the part 131. It will benoted that the sealing ring 136 is disposed between the annulus of pins138 (only one pin 138 is actually shown in FIG. 3) and the radiallyoutermost portion of the chamber 130. The starter gear 140 surrounds acylindrical seat 139 forming part of the peripheral surface of theportion 132a. The gear 140 serves its primary purpose and also as ameans for holding the properly inserted pins 138 against movementradially and away from the axis of the flywheel 3.

It is clear that the connection between the parts 131, 132 of theflywheel 3 which is shown in FIG. 3 can be used with equal or similaradvantage between the parts 31, 32 of the flywheel 3 which is shown inFIG. 1 as well as between analogous parts of flywheels in otherembodiments of the improved apparatus. In other words, the connection ofFIG. 3 can be used between parts which are made by casting or in sheetdeforming or like machines.

An advantage of housing parts which are made of deformable metallicsheet material is that they can be produced at a fraction of the cost ofmaking such parts in a casting machine or in a material removingmachine. Moreover, the making of such parts of deformable metallic sheetmaterial renders it possible to impart thereto practically any desiredshape. The shaping operation can be carried out in a stamping,embossing, drawing, coining or other suitable machine. The making of oneor both parts of the housing for the chamber 130 from such materials isespecially desirable and advantageous when the compartment for the coilsprings of the outer damper and/or the compartment for the coil springsof the inner damper is not a complete annulus, e.g., if the parts orsections of the housing must be provided with constrictions of the typeshown, for example, in FIG. 5. Still further, such mode of making theparts of the housing renders it possible to produce the aforediscussedabutments or stops (corresponding to the abutments 55, 55a and 65, 66shown in FIG. 1) of the flywheel 3 as integral constituents of therespective sections or parts. This obviates the need for the utilizationof rivets 58, 67 and analogous fasteners and contributes significantlyto lower initial and assembly cost of the entire apparatus.

Proper angular positioning of the parts or sections 131, 132 relative toeach other can be ensured by providing the cylindrical surfaces 134, 135with non-uniformly distributed holes or bores for the centering pins138, i.e., by selecting the distribution of the holes in such a way thateach hole in the surface 134 registers with a hole in the surface 135only in a single angular position of the part 131 with reference to thepart 132.

The sealing device 174 is located radially inwardly of the inner damperbetween the sections or parts 131, 132. Thus, the coil springs of theinner damper are or can be contacted by the viscous fluid medium.However, it is also possible to install one or two sealing devicesbetween the compartment for the coil springs 145 and the compartment forthe coil springs 148, i.e., the inner damper can remain dry.

FIGS. 4 and 5 show a portion of a third apparatus 201 wherein thehousing for the chamber 230 includes two parts 231, 232 each of which ismade of a deformable metallic sheet material. The parts 231, 232 areportions of the flywheel 3. The radially outermost portions of the parts231, 232 are permanently connected to each other at 238, e.g., bywelding. This even more reliably ensures that the surfaces 234, 235 ofthe parts 231, 232 remain in permanent sealing engagement with eachother and this also obviates the need for a sealing ring (such as 36 or136). The permanent connection at 238 can be established in an electronbeam welding, resistance butt welding, pressure welding or othersuitable welding machine. The radially innermost portion of the part 231is connected with an axial extension 220 of the flywheel 3 whichperforms the function of the protuberance 20 shown in the apparatus ofFIGS. 1-2 and is surrounded by the antifriction bearing means 16. Theextension or protuberance 220 has a centering seat 220b for the part 231of the flywheel 3, and the part 231 abuts a radially extending shoulder220c of the extension 220. Rivets 200 are provided to ensure that thepart 231 remains in contact with the shoulder 220c. These rivets can bereplaced by welds analogous to the connections 238 between the surfaces234, 235 of the parts 231 and 232. Alternatively, a portion of theextension 220 can be upset to the left of the radially innermost portionof the part 231 to thus establish a permanent and wobble-free connectionbetween 220 and 231.

If the parts which form the housing for the chamber 30, 130 or 230 aremade of deformable metallic sheet material, the aforediscussed abutmentsor stops for the coil springs of the inner and/or outer dampers in therespective chambers can constitute integral parts of the housing. Thisis shown in FIG. 5 wherein the abutments 255, 255a are integral parts of231, 232, respectively. These abutments resemble pockets which areformed as a result of suitable deformation of the corresponding parts231 and 232. This simplifies the making and assembly of the apparatus,i.e., the number of parts which must be separately produced andassembled is reduced considerably.

For the purpose of satisfactory welding, the material (such as steel) ofthe parts or sections 231, 232 should have a relatively low carboncontent. It suffices if the carbon content is low in those regions ofthe surfaces 234, 235 which are actually welded to each other (at 238).

The apparatus 301 which is shown in FIGS. 6, 6a, 7 and 7a againcomprises a composite flywheel having two discrete components orflywheels 3, 4 which are rotatable relative to each other with therespective races of an antifriction ball bearing 16. The means forholding the flywheels 3 and 4 against axial movement away from eachother comprises a ring-shaped retainer 322 which is affixed to the endface of the axial protuberance 320 of the flywheel 3 by a set of rivets322a or the like. The manner in which the flywheels 3, 4 are assembledwith each other is or can be the same as described in connection withFIGS. 1 and 2. Thus, the antifriction bearing 16 can be mounted in theflywheel 4 and is thereupon pushed onto the protuberance 320 of theflywheel 3 so that its inner race surrounds the cylindrical surface 320aat the periphery of the protuberance 320. A sealing device 374 ismounted on the flywheel 3 (i.e., on the flywheel which is nearer to theoutput element of the engine) before the protuberance 320 is insertedinto the axial recess of the flywheel 4. The connection 342 between theradially innermost portion of the flange 341 and the radially outermostportion of the disc 327 facilitates assembly of the apparatus 321. Theflange 341 again constitutes the output element of the outer damper 13as well as of the output element of the inner damper 14. The disc 327 issecured to the flywheel 4 by rivets 326.

The parts 331, 332 which constitute the housing for the chamber 330 arecastings. The radially outermost portion 332a of the part 332 is acylinder having a cylindrical internal surface 335 which is adjacent asealing ring 336 and surrounds the complementary cylindrical externalsurface 334 of the part 331 so that the latter centers the part 332 andits cylindrical portion 332a. Radially extending pins 338 are providedto hold the parts 331, 332 against axial movement away from each other;such pins are received in registering bores or holes provided thereforin the cylindrical surfaces 334 and 335. The starter gear 340 surroundsthe cylindrical portion 332a and prevents expulsion of the pins 338 fromtheir respective bores.

The torque transmitting connection 342 again comprises tooth-likeprojections 372 which extend radially inwardly from the internal surfaceof the flange 341 and complementary tooth-like projections 373 which areprovided on the disc 327 and mate with the projections 372.

FIG. 6a shows the details of the sealing device 374 which is installedbetween the radially innermost portion of the part 332 one the one handand the axial protuberance or projection 343 of the flywheel 4 and disc327 on the other hand. The device 374 comprises a washer-like sealingmember 375 which is elastically deformable in the axial direction andhas an inner portion engaging a ring-shaped insert 376 on the projection343. The outer portion of the sealing member 375 is coupled to theradially innermost portion of the part 332 so that it is held againstmovement in the axial direction of the apparatus 301. The sealing member.375 is deformable not unlike a diaphragm spring and its radiallyoutermost and innermost portions are coated with layers 3.75a, 375bwhich can consist of or contain synthetic plastic material and can beapplied by spraying. The material of the layers 375a, 375b should have alow coefficient of sliding friction and should exhibit a certain amountof elastic or plastic deformability. A ring-shaped coupling andcentering member or carrier 380 is provided on the part 332 and isconfigurated to form an annular groove or socket receiving the radiallyoutermost portion (including the layer 375a) of the sealing member 375.The confinement of the radially outermost portion of the sealing member375 in the groove or socket which is defined by the carrier 380 is suchthat the sealing member 375 can change its conicity. That portion (380b)of the carrier 380 which defines the aforementined groove or socket isreceived in a ring-shaped centering notch 377 provided therefor in theradially innermost portion of the part 332. The carrier 380 comprisestwo radially outwardly extending collars 380a which flank the annularinnermost portion 332b of the part 332 so as to securely locate thecarrier 380 in a desired axial position. The carrier 380 can be said toconstitute a swivel bearing for the sealing member 375 of the sealingdevice 374.

The ring-shaped insert 376 has a surface which is adjacent a surface ofthe sealing member 375 to form therewith a seal against penetration offoreign matter into the radially innermost portion of the chamber 330 aswell as against escape of viscous fluid medium from the chamber. Adisc-shaped radially innermost portion 376a of the insert 376 is clampedbetween the projection 343 of the flywheel 4 and the disc 327, and adished radially outermost portion 376b of the insert 376 engages theradially innermost portion of the sealing member 375 so that the latteris held in axially stressed position and the insert and sealing memberdefine the aforementioned seal at the radially innermost locus of thechamber 330.

The portions 376a and 376b of the insert 376 are offset with referenceto each other in the axial direction of the apparatus 301 in such a waythat the portion 376a is immediately adjacent the tooth-like projections373 of the disc 327 but the portion 376b is axially offset in adirection away from the disc 327 and toward the flywheel 4. The insert376 cooperates with the sealing member 375 not only to seal the radiallyinnermost portion of the chamber 330 from the atmosphere but also toseal such radially innermost portion of the chamber 330 from theradially extending ventilating channel 368 between the parts 331, 332 onthe one hand and the flywheel 4 on the other hand.

In order to facilitate assembly of the flywheels 3 and 4 into theapparatus 301 which is shown in FIGS. 6 and 7, the inner diameter of thesealing member 375 exceeds the outer diameter of the annulus includingthe radially outwardly extending tooth-like projections 373 which areprovided on the disc 327 and form part of the connection 342. Theportion 376b of the insert 376, which is in engagement with and stressesthe sealing member 375 in the axial direction of the apparatus 301,extends radially outwardly beyond the tooth-like projections 373 of thedisc 327.

When the antifriction bearing 16 is slipped onto the cylindrical portion320a of the peripheral surface of the protuberance 320 on the flywheel3, the projections 373 move into mesh with the projections 372 of theflange 341 to thereby establish the connection 342. At the same time,the portion 376b of the insert 376 engages and stresses the sealingmember 375 to ensure the establishment of a seal between 376b and 375b.

In order to prevent or reduce wear upon the surfaces which bound theannular compartment 351 (including the grooves 352, 353 in the parts331, 332) of the chamber 330 and are contacted by the convolutions ofcoil springs 345 forming part of the outer damper 13 in the chamber 330,there is provided a strip- or band-shaped frictional engagement reducingmember or insert 381 of hardened metallic material (such as steel). Themember 381 surrounds the radially outermost portion of the compartment351 and is adjacent the radially outermost portions of the coil springs345. In accordance with a presently preferred embodiment, the member 381constitutes a short cylinder which is received in a shallow recess 382provided therefor in the part 331 of the flywheel 3. The recess 382 canbe formed during casting of the part 331 or is machined into the part331 thereafter. When the apparatus 301 rotates, the convolutions of thecoil springs 345 tend to move radially outwardly under the action ofcentrifugal force and thus bear against the internal surface of themember 381. The manner in which the member 381 is secured againstslippage with reference to the flywheel 3 is shown in FIG. 7a. Thus, themember 381 is a split ring with end portions 381a bent radiallyoutwardly into a notch 383 provided in the part 331 of the flywheel 3.

The circumferential abutments or stops 355, 355a for the coil springs345 of the outer damper 13 and the circumferential abutments or stops365, 366 for the coil springs 348 of the inner damper 14 in the chamber330 are separately produced forgings, stampings or like elements whichare respectively provided with one-piece rivets 358, 367 for attachmentto the respective parts 331, 332 of the flywheel 3.

FIG. 7 shows that the abutments 355, 355a which flank the arms 344 ofthe flange 341 extend beyond the respective arms 344 in thecircumferential direction of the flywheel 3. In the idle or neutralposition which is shown in FIG. 7, the arms 344 are disposed centrallyof the respective abutments 355, 355a, i.e., such abutments extendcircumferentially beyond both ends of the respective arms 344 throughidentical distances.

The abutments 365, 366 which flank the radially extending webs 350 ofthe flange 341 also extend circumferentially beyond the respective webs350. The webs 350 alternate with the coil springs 348 of the innerdamper 14 in the chamber 330. In contrast to the positions of abutments355, 355a with reference to the respective arms 344 in the idle positionof the flange 341, the abutments 365, 366 then extend beyond one endonly of the respective webs 350 (as seen in the circumferentialdirection of the flywheel 3). The other end of each web 350 can be flushwith the respective ends of the associated abutments 365, 366. Theselection of the circumferential offset of the abutments 365, 366 andthe respective webs 350 relative to each other is such that theneighboring abutments 365 as well as the neighboring abutments 366 areoffset in opposite directions. This ensures that the inner coil springs348 (there are four coil springs 348) form two groups 348a, 348b whichbecome effective during different stages of angular displacement of theflywheels 3, 4 relative to each other.

The chamber 330 again contains a supply of viscous fluid medium (such assilicon oil or grease) which should at least fill the compartment 351when the apparatus 301 is rotated. It is presently preferred to selectthe quantity of fluid medium in such a way that it not only fills thecompartment 351 but also contacts at least the radially outermostportions of the coil springs 348 when the flywheels 3 and 4 are driven.A filling to the level such that the supply of fluid medium extendsradially inwardly to the axes of the coil springs 348 has been found tobe quite satisfactory.

Cup-shaped spring retainers 359 are installed in the compartment 351between the arms 344 and abutments 355, 355a on the one hand and therespective end portions of the coil springs 345 on the other hand. Thedimensions of the retainers 359 are or can be selected in such a waythat they at least substantially fill the respective portions of thecompartment 351, i.e., the retainers 359 can act not unlike pistons whenthey are caused to move along the surfaces bounding the compartment 351or vice versa. This ensures that the retainers 359 can produce adesirable damping action by throttling the flow of viscous fluid mediumbetween their peripheries and the surfaces bounding the respectiveportions of the compartment 351. The damping action is or can be thesame as described in connection with FIGS. 1 and 2.

Each cup-shaped retainer 359 is provided with a slightly conicalextension or stub 359a which normally extends into the adjacent endconvolutions of the respective coil spring 345. This can be seen in thetop portion of FIG. 7. Each stub 359a has a tip 359b which is conicalbut can also be roof-shaped. The just described design of the retainers359 ensures that the stubs 359a automatically find their way back intothe end convolutions of the adjacent coil springs 345 even if the stubs359a are completely separated from the neighboring springs 345 duringcertain stages of angular movement of the flywheels 3 and 4 relative toeach other. Thus, when a spring 345 is free to expand, its endconvolutions automatically receive the stubs 359a of the adjacentretainers 359, and the same holds true when the retainers 359 movetoward the adjacent end portions of the respective coil springs 345.This not only guarantees a more reliable operation but also reduces thelikelihood of damage to the springs 345 and/or to the retainers 359. Thestubs 359a of the retainers 359 are likely to leave the adjacent endportions of the respective coil springs 345 when the springs 345 arecompressed and the apparatus 301 is driven at a relatively high RPM.Under such operating conditions, friction between the convolutions ofthe springs 345 and the adjacent surfaces bounding the compartment 351of the chamber 330 is or can be so pronounced that the springs 345cannot expand or cannot fully expand in immediate response to an abruptchange of load. During such abrupt change of load, the arms 344 of theflange 341 displace the viscous fluid medium in the compartment 351 andthe fluid medium thereupon flows back radially outwardly under theaction of centrifugal force. Such flow of fluid medium during an abruptchange of load and the resulting angular displacement of the flywheels3, 4 relative to each other can result in expulsion of stubs 359a of theretainer 359 from the adjacent end portions of the respective coilsprings 345 because the springs 345 are slow to expand for theaforediscussed reasons.

It will be noted that the layer or coating 375a on the radiallyoutermost portion of the sealing member 375 is not in the path of flowof viscous fluid medium radially inwardly in response to an abruptangular displacement of the flywheel 3 relative to the flywheel 4 and/orvice versa. This ensures that the fluid medium (e.g., grease) whichflows radially inwardly along the right-hand side of the flange 341 (asseen in FIG. 6 or 6a) cannot penetrate into the notch 377 of the part332 to escape into the channel 368 between the part 332 and the flywheel4. The notch 377 is sufficiently deep (as seen in the axial direction ofthe flywheels) to ensure that the major part at least of the layer 375acan be received threin to thus maintain the sealing member 375 away fromthe path of the fluid medium when the latter flows radially inwardlyalong the sealing device 374. An additional advantage of theconstruction which is shown in FIG. 6a is that, when the fluid medium inthe chamber 330 is pressurized in response to abrupt angulardisplacement of the flywheels relative to each other, the fluid mediumacts upon the entire left-hand side of the sealing member 375 so as tourge the latter into a more pronounced sealing engagement with the part332 (at 375a) as well as against the flywheel 4 (i.e., against theinsert 376 which can be said to constitute a portion of the flywheel 4).Thus, the sealing action of the member 375 is enhanced in automaticresponse to pressurization of fluid medium in the chamber 330.

The apparatus 301 operates as follows:

When the flywheel 4 is caused to turn with reference to the flywheel 3so that it leaves the idle position of FIG. 7, the flange 341 iscompelled to rotate through the medium of the connection 342 (i.e., theprojections 373 of the disc 27 on the flywheel 4 transmit torque to theprojections 372 of the flange 341). This results in compression of coilsprings 348 which form the group 348b because the corresponding webs 350of the flange 341 move with reference to the abutments 365, 366 on theparts 331, 332 of the flywheel 3. When the flywheel 4 completes anangular displacement through the angle 379 in one direction or throughthe angle 390 in the opposite direction, the webs 350 of the flange 341(which turns with the flywheel 4) engage the adjacent ends of the coilsprings 348 which form the group 348a so that, if the flywheel 4continues to turn with reference to the flywheel 3, the coil springs 348of the group 348a are compressed and store energy jointly with the coilsprings 348 of the group 348b. When the flywheel 4 thereupon completesan additional angular displacement through the angle 379a in onedirection or through the angle 390a in the opposite direction, the arms344 of the flange 341 engage and begin to compress the respective coilsprings 345 so that the springs 345 begin to store energy (or to storeadditional energy, depending upon their initial condition) because theyare acted upon by the arms 345 in conjunction with the respectiveabutments 355, 355a on the parts 331, 332 of the flywheel 3. In theembodiment which is shown in FIGS. 6 to 7a, the angle 379 equals orclosely approximates the angle 379a, and the angle 390 equals or closelyapproximates the angle 390a. Thus, the coil springs 345 store energysimultaneously with the coil springs 348 of the group 348a. Therefore,the characteristic curve of these springs is a two-stage curve.

It is equally within the purview of the invention to design theapparatus 301 in such a way that the angles 379, 390 merely approximatethe respective angles 379a, 390a or that the angles 379, 390 areentirely different from the angles 379a, 390a, respectively, i.e., thecharacteristic curve can have three or more stages or steps in onedirection of rotation and two stages or steps in the opposite directionor the characteristic curve can have more than two stages or steps inone direction and three or more stages or steps in the oppositedirection.

The arrangement may be such that each coil spring 345 begins to storeenergy during a different stage of angular displacement of the flywheelsrelative to each other. The same applies for the coil springs 348 of theinner damper. This applies regardless of whether the dampers areconnected in series or in parallel.

It is further possible to shift the abutments 365, 366 with reference tothe coil springs 348 of the group 348b to positions corresponding tothat which is shown in FIG. 7 by phantom lines, as at 365a, to thusensure that the bias of the springs 348 in the group 348b does notchange in immediate response to angular displacements of the flywheel 3and/or 4 from the idle position of FIG. 7 in either direction. At suchtime, the apparatus 301 merely produces a hydraulic or viscous dampingaction and/or a frictional damping action.

The magnitude or characteristics of the hydraulic or viscous dampingaction can be varied in a number of ways. For example, the number ofcup-shaped retainers 359 can be reduced (i.e., only certain coil springs345 can be provided with such retainers or only one end of each coilspring can be provided with a retainer). Furthermore at least one coilspring 348 in the group 348a and/or 348b can be provided with one or twocup-shaped retainers corresponding to the retainers 359 or analogousretainers. Other factors which influence the hydraulic or viscousdamping action include the selected quantity of fluid medium in thechamber 330 and/or the width of the clearance or gap between the flange341 and the portion 360 or 361 of the surface on the part 331 or 332 ofthe flywheel 3. Additional damping action is produced as a result ofturbulence of the viscous fluid medium in the chamber 330. The exactmanner in which such damping action is produced is the same as describedin connection with FIGS. 1 and 2.

FIG. 7 shows that the outer damper 13 of the apparatus 301 comprisesfour equidistant coil springs 345 and the inner damper 14 comprises fourequidistant coil springs 348. Each of the coil springs 345 extends alongan arc of or close to 78 degrees, each coil spring 348 in the group 348bextends along an arc of or close to 74 degrees, and each coil spring 348of the group 348a extends along an arc of or close to 68 degrees. Thus,the four coil springs 345 jointly extend along approximately 86 percentof a complete circle, and the four coil springs 348 jointly extend alongapproximately 79 percent of a complete circle.

The flywheel 4 includes a portion 4b which has radially outwardlyextending projections or lugs 386 (FIG. 7) each of which has a tappedaxially parallel bore 387 to facilitate the attachment of a frictionclutch. One or more lugs 386 are further provided with bores or holes388 which are parallel to the respective tapped bores 387 and serve forreception of pins (not shown) which facilitate centering of the clutchcover on the flywheel 4 during assembly of the friction clutch with theflywheel 4.

The lugs 386 contribute to a reduction of the weight of the flywheel 4as a result of removal or absence of material in recesses or toothspaces 386a which alternate with the lugs 386, as seen in thecircumferential direction of the flywheel 4. Moreover, the recesses 386aprovide paths for the flow of air which cools the flywheel 4, the supplyof fluid medium in the chamber 330 and the clutch which is affixed tothe flywheel 4. Atmospheric air which flows through the recesses 386acontacts the flywheel 4 and the aforementioned cover of the clutch whichis attached to the flywheel 4 by threaded fasteners extending into thetapped bores 387 of the lugs 386. The flywheel 4 is further formed withair-conveying passages 369 which communicate with the radially innermostportion of the channel 368 between the flywheels 3 and 4.

The thickness of the lugs 386 on the portion 4b of the flywheel 4 canexceed the thickness of the remaining portion of the flywheel 4. Suchdesign of the flywheel 4 can be resorted to in order to ensure that themass or weight of the flywheel 4 will equal or approximate a preselectedvalue and/or to prevent overheating of the portion 4b (which isoutwardly adjacent the friction surface 4a).

The damping action which is provided by the viscous fluid medium can befurther varied by forming the parts 331, 332 of the flywheel 3 withgrooves 352, 353 which have portions of different cross-sectional areas.Thus, the compartment 351 can include at least one portion of largercross-sectional area and at least one portion of smaller cross-sectionalarea. The damping action in the portion or portions of largercross-sectional area is less pronounced. The compartment 351 can beconfigurated in the just described manner in the region of one, two,three or all four coil springs 345. The portions of largercross-sectional area can be provided anywhere along the length of one ormore coil springs 345 but are preferably provided in regions receivingthe end portions of the coil springs 345 when such springs are notcompressed or store a minimum of energy. The transitions from theportions of smaller cross-sectional area to the portions of largercross-sectional area or vice versa can be gradual or abrupt. It ispresently preferred to provide the enlarged portions of the compartment351 in the region or regions of the smaller-diameter portion of suchcompartment. This can be seen in FIG. 7, as at 389, where the enlargedportion of the cross-sectional area of the compartment 351 is close tothe axis of the composite flywheel 3+4 and includes a first part withabrupt transition from the larger cross-sectional area to the smallercross-sectional area as well as a portion with a gradual transition. Theenlarged portion of the compartment 351 can be formed by removingmaterial from the part 331 or 332 of the flywheel 3 and/or from theflange 341 (this is actually shown in FIG. 7). The damping action ofviscous fluid medium can be varied within a rather wide range byappropriate selection of the length and/or cross-sectional area of theenlarged portion or portions of the compartment 351, i.e., by enlargingone or more portions of the groove 351 and/or 352 and/or by removingmore or less material from the flange 341 in the region of the outerdamper 13.

FIG. 8 shows a portion of an apparatus 401 wherein the part 432 of thehousing for the chamber which confines the inner and outer dampers has acircumferentially complete groove 460 for a sealing ring 460a. Thesealing ring 460a is elastic in the radial direction and can constitutean open wire ring or it can be made of a synthetic plastic material. Thecross-sectional configuration of the groove 360 is oval or otherwiseelongated and this groove extends at an angle outwardly from the locus(adjacent the flange 441) where it ends in the left-hand side or surfaceof the part 432. The sealing ring 460a tends to contract to normallyengage the adjacent side or surface of the flange 441, but the ring 460aexpands under the action of centrifugal force when the RPM of theapparatus 401 is increased so that it ceases to establish a seal betweenthe part 432 and the flange 441. This entails an increase in theeffective cross-sectional area of the clearance or gap 454 between theflange 441 and the part 432, i.e., the sealing action of the ring 460ais reduced br terminated and the gap 454 offers a lesser resistance tothe flow of viscous fluid medium into and from the radially outermostportion (compartment 451) of the chamber which is defined by the parts431 and 432. The diameter of the sealing ring 460a is reducedautomatically when the RPM of the apparatus 401 is reduced so that theviscous fluid medium urges the sealing ring into more pronounced sealingengagement with the flange 441 in response to increasing angulardisplacement of the .one flywheel relative to the other and/or viceversa.

The part 531 of that flywheel which is affixed to the output element ofthe engine has an axial extension 431a in the form of a short cylinderwhich surrounds the radially outermost portion of the part 432. Theextension 431a serves as a means for centering the part 432 and it alsocooperates with the sealing ring 436 to prevent escape of fluid mediumfrom the compartment 351 radially outwardly between the abutting sidesor surfaces of the parts 431 and 432.

The apparatus 501 of FIG. 9 comprises a strip- or band-shaped frictionalengagement reducing member or insert 581 which corresponds to the member381 of the apparatus 301 and has an arcuate cross-sectional outline witha concave side facing the coil springs 545. This member is made of ahard or hardened material which can resist extensive wear as a result ofrepeated frictional engagement with the convolutions of the coil springs545 in the compartment 551. The member 581 can be made of steel and canbe hardened in any suitable way. The curvature of the concave side ofthe member 51 preferably equals or approximates the curvature ofconvolutions of the adjacent springs 545. As shown in FIG. 9, the member581 can surround the radially outermost portion of the compartment 551along an arc of approximately 90 degrees; this member is received inshallow recesses 531a, 532a which are provided therefor in therespective parts 531, 532 of the housing which forms part of theleft-hand flywheel and defines the chamber for the inner and outerdampers. The aforementioned are can be in the range of 45-120 degrees,preferably 60-90 degrees.

Instead of using a member 581 which is hardened, either entirely oralong its surface, one can employ a member which has a relatively softcore and a coating of highly wear-resistant material such as hard orsolid nickel or chromium. It is also possible to make the member 581 ofa highly wear-resistant plastic material.

The apparatus 501 of FIG. 9 exhibits the advantage that the useful lifeof the flywheel which is connected with the output element of the engineor of the entire apparatus can be prolonged by the simple expedient ofreplacing a worn or damaged member 581 with a fresh member. In otherwords, the parts 531, 532 (which can constitute solid castings) are notsubject to any wear, or to extensive wear, because they are not inintensive friction engagement with the coil springs 545.

The means for coupling the parts 531 and 532 to each other comprises aring-shaped member or cage 533 which is or can be made of suitablemetallic sheet material and surrounds the radially outermost portion532b of the part 532 as well as a portion 531a of the part 531 adjacentthe starter gear 540. The radially inwardly extending portions 533a and533b are integral with a cylindrical web of the cage 533 and flank theportions 531b, 532b:to thus prevent the parts 531, 532 from movingaxially and away from each other.

The means for preventing angular displacements of the parts 531, 532relative to each other comprises axially parallel centering members orpins 538 each of which can constitute a so-called heavy type dowel pinand which are received in registering axially parallel bores or holes ofthe portions 531b, 532b. The radially inwardly extending portions 533aand 533b of the cage 533 hold the pins 538 against axial movement. Theleft-hand radially extending portion 533a of the cage 533 is adjacentthe starter gear 540 which is connected to and surrounds the part 531.

The utilization of a frictional engagement reducing member in the formof a strip or band having a concave side or surface which is adjacentthe convolutions of the coil springs 545 is desirable and advantageousbecause this greatly enlarges the area of contact between the member 581and the coil springs with attendant reduction of pressure per unit areaof the abutting surfaces and a considerable reduction of wear. Itnormally suffices if the member 581 extends around the coil springs 545along an arc of between 45 and 120 degrees, normally between 60 and 90degrees.

The one-piece member 581 (or the one-piece member 381 of FIG. 6) can bereplaced with a composite member including a plurality of arcuateportions each of which is or can be separately embedded in the housingfor the damper or dampers. The length of each arcuate portion can equalor approximate the maximum length of a coil spring in the respectivecompartment (as measured in the circumferential direction of theflywheels).

The flywheel 3 of the apparatus 601 which is shown in FIG. 10 comprisesa housing including the parts 631 and 632 which define an annularchamber 630 for the inner damper 14 and the outer damper 13. The coilsprings 645 (only one shown) of the outer damper 13 are installed in thecompartment 651 of the chamber 630. The dampers 13, 14 are connected inseries. One coil spring of the inner damper 14 is shown at 648. Theparts 631, 632 constitute the input element of the outer damper 13 andare provided with abutments or stops 655, 655a for the end portions ofthe coil springs 645. As shown, the abutments 655 and 655a arerespectively riveted to the parts 631 and 632.

A flange 641 constitutes the output element of the outer damper 13 andthe input element of the inner damper 14.

The apparatus 601 further comprises disc-shaped members in the form ofwashers 665, 666 which flank the flange 641 radially inwardly of thecompartment 651 and are rigidly connected to each other by distancingelements in the form of rivets 667 which are anchored in the flywheel 4.The washers 665, 666 are provided with windows 665a, 666a which registerwith windows 641a in the flange 641 and receive the coil springs (energystoring elements) 648 of the inner damper 14. The coil springs 648 serveto yieldably oppose angular movements of the flange 641 and washers 665,666 relative to each other. The flange 641 is further provided withradially outwardly extending arms 644 which alternate with the coilsprings 645 of the outer damper 13, i.e., the arms 644 extend into thecompartment 651 of the chamber 630.

The apparatus 601 also comprises an antifriction ball bearing 16 whichis installed between the flywheels 3 and 4 in the same way as describedin connection with FIGS. 1 and 2. A sealing device 674 operates betweenthe radially innermost portion of the part 632 and the adjacent portionof the washer 666. The parts 631 and 632 are formed with grooves whichjointly define the compartment 651 as well as a second compartment forportions of the coil springs 648.

A friction generating device 690 is provided between the flywheels 3 and4 adjacent the antifriction bearing 16. This device is also confined inthe chamber 630 and surrounds the protuberance 620 of the flywheel 3between the bearing 16 and washer 665 on the one hand and the radiallyextending portion 961 of the section or part 631 on the other hand. Thefriction generating device 690 comprises a prestressed energy storingelement 692 which is composed of two neighboring diaphragm springs andoperates between the inner race of the bearing 16 and apressure-applying ring 693. A friction pad 694 in the form of a washeris disposed between the ring 693 and the radially innermost portion 691of the part 631. The pad 694 can be made of synthetic plastic materialand has radially outwardly extending projections or prongs 694a whichalternate with spaces for the heads 667a of the aforementioneddistancing elements or rivets 667. The spaces between the prongs 694aprovide room for some angular movement of the pad 694 relative to theflywheel 4 and vice versa. Thus, the flywheel 4 can turn the pad 694with reference to the adjacent flywheel 3 when the heads 667a of rivets667 come into abutment with the prongs 694a at the one or the other endof the respective spaces between prongs 694a. It will be noted that,when the direction of angular movement of the flywheel 4 relative to theflywheel 3 or vice versa is reversed, the friction generating device 690is ineffective during the initial stage of angular movement of theflywheel 3 or 4 in the opposite direction. The extent of that angulardisplacement of the flywheel 3 or 4 during which the friction generatingdevice 690 is ineffective is determined by the diameters of the heads667a of the rivets 667 and by the length of the spaces betweenneighboring prongs 694a (as seen in the circumferential direction of theflywheels 3 and 4). The play between the heads 667a of the rivets 667and the prongs 694a of the friction pad 694 renders it possible to shiftthat portion of the total angular displacement of the flywheel 3relative to the flywheel 4 and/or vice versa during which the frictiongenerating device 690 is effective with reference to the angularpositions in which the energy storing coil springs 645, 648 begin tostore energy.

Confinement of the friction generating device 690 in the chamber 630 isdesirable and advantageous because this ensures that the moment offriction which is generated by the device 690 is constant or practicallyconstant during the entire useful life of the apparatus 601.

It is possible to dimension the prongs 694a of the friction pad 694and/or the heads 667a of the rivets 667 in such a way that the pad 694is compelled to share all angular movements of the flywheel 4, i.e.,that the friction generating device 690 is effective during each andevery stage of angular movement of the flywheel 3 relative to theflywheel 4 and/or vice versa. Alternatively, the friction pad 694 can beextended radially outwardly into the region of the coil springs 648 andcan have one or more windows for a corresponding number of coil springs648. This enables the coil spring or springs 648 in such window orwindows to restore the angular position of the friction pad 694, eitherentirely or in part.

The radially outermost portions 631b, 632b of the parts 631, 632 arecoupled to each other by a ring-shaped cage 633 which is or can be madeof a metallic sheet material. The radially inwardly extending portionsof the cage 633 flank the portions 631b, 632b of the parts 631 and 632to thereby hold such parts against axial movement away from each other.The means for holding the parts 631, 632 against rotation relative toeach other comprises axially parallel pins 638, such as heavy type dowelpins, which are received in registering bores or holes of the portions631b, 632b. Each pin 638 further extends into a registering bore or holein the right-hand radially extending portion 633b of the cage 633. Thus,the pins 638 also serve to hold the cage 633 against angular movementrelative to the parts 631, 632 of the flywheel 3; this is desirablebecause the cage 633 is provided with means (to be describedhereinafter) which limits the extent of angular movability of theflywheels 3 and 4 relative to each other.

The radially inwardly extending portion 633b of the cage 633 is disposedbetween the flywheel 4 and the part 632 and its radially innermost parthas profiled portions in the form of teeth 633c which cooperate withpin- or stud-shaped projections 658 on the flywheel 4 to determine theextent of angular movability of the flywheels 3 and 4 relative to eachother. The projections 658 cannot move with reference to the flywheel 4and the cage 633 and its teeth 633c cannot move relative to the flywheel3 (because the pins 638 are anchored in the parts 631, 632 as well as inthe portion 633b of the cage 633). The projections 658 (each of whichcan constitute a dowel pin) cooperate with the teeth 633c to determinethe extent of angular movability of the flywheels 3, 4 relative to eachother and they also serve as a means for centering the cover (not shown)of a friction clutch which can be mounted on the flange 4a of theflywheel 4 in the same way as described in connection with FIGS. 1 and2. The left-hand end portions of the projections 658 extend into theradially outermost portion of the radially extending ventilating channel668 between the flywheel 4 and the part 632. The channel 668communicates with passages 669 which are provided in the flywheel 4radially inwardly of the inner damper 14.

The friction generating device 690 (or an analogous friction generatingdevice) and/or the cage 633 (or an analogous cage) with means (633c) forlimiting the extent of angular movability of the flywheels 3 and 4relative to each other can be employed with equal or similar advantagein apparatus wherein the dampers 13, 14 are connected in parallel ratherthan in series. For example, the friction generating device 690 and thecage 633 with its teeth 633c can be used in the apparatus 1 of FIGS. 1and 2.

Referring to FIGS. 11 and 12, there is shown an apparatus 701 having acomposite flywheel 702 with two components or flywheels 703 and 704.Antifriction bearing means 15 is interposed between the flywheels 703,704 which can rotate relative to each other. The flywheel 703 includes ahousing which defines an annular chamber 730 for a damper 713. Thehousing of the flywheel 703 includes two sections or parts 731, 732having radially outermost portions which are outwardly adjacent thechamber 730 and are connected to each other. Each of the parts 731, 732can be made of deformable metallic sheet material and their radiallyoutermost portions can be bonded (e.g., welded) to each other, as at738. The weld 738 simultaneously serves as a means for sealing theradially outermost portion of the chamber 730 from the surroundingatmosphere. The welding operation can be carried out in a resistancebutt welding machine or in a so-called stored-energy high-rate dischargewelding machine. In each of these machines, the welding operation iscarried out by placing the parts to be welded against each other and byapplying to them low-voltage high-amperage alternating current to heatthe parts to welding temperature and to unite such parts in response tothe application of pressure. In order to allow for the carrying out ofsuch welding operation, the parts 731, 732 of the flywheel 703 areprovided with surfaces 734, 735 which can be placed into abutment witheach other and each of which has a predetermined area for the requiredcurrent strength. The surfaces 734, 735 are welded to and abut eachother in a plane which extends at right angles to the axis of thecomposite flywheel 702.

In order to properly center the part 732 relative to the part 731 in thecourse of the welding operation, the part 731 comprises a cylindricalportion 731a which surrounds the cylindrical peripheral surface 735a ofthe part 732. Accurate angular positioning of the parts 731, 732relative to each other during welding of the surfaces 734, 735 to eachother is ensured by welding pins (not shown) which project into axiallyparallel recesses or sockets 765, 766 of the parts 731, 732 in thecourse of the welding operation. This ensures that the parts 731, 732are bonded to each other in optimum angular and radial positions.

The making of the weld 738 between the surfaces 734, 735 of parts 731,732 involves a certain axial displacement of these parts relative toeach other. Therefore it may be desirable or advantageous to provide thepart 731 and/or 732 with one or more axially extending stops whichbecome effective only in the course of the welding operation. FIG. 11shows, by broken lines, a stop 767 which is provided on the part 732 ofthe flywheel 703. The provision of stops 767 renders it possible to makethe quality of the welding operation less dependent upon the exactcurrent strength, i.e., it is possible to operate with greater currentstrengths because the axial positions of parts 731, 732 with referenceto each other are determined by the stops 767 rather than by theselected current strength and the axial pressure which is applied to theparts 731, 732 in the course of the welding operation.

The output element of the damper 713 is a radially disposed flange 741which is installed between the parts 731, 732 of the flywheel 703. Theconnection 742 between the radially innermost portion of the flange 741and a disc 727 at the end face of the axial protuberance or projection743 of the flywheel 704 is of such nature that the flange 741 can moveaxially with reference to the disc 727 and vice versa. The means forsecuring the disc 727 to the projection 743 (which extends toward thepart 731 of the flywheel 703) includes rivets 726 or analogous fastenermeans.

The flange 741 is formed with radially outwardly extending arms 744which alternate with the energy storing coil springs 745 of the damper713 and extend into the annular compartment 751 of the chamber 730. Thecompartment 751 constitutes the radially outermost portion of thechamber 730 and receives the coil springs 745. This compartment includestwo annular grooves 752, 753 which are respectively provided in theradially extending surfaces of the parts or sections 731, 732 at thelevel of the damper 713. The making of grooves 752, 753 presents noproblems since the parts 731, 732 consist of a deformable metallic sheetmaterial. The central portions of the coil springs 745 (as seen in theaxial direction of the apparatus 701) are located in the plane of theflange 741, and the outer portions of such springs extend into therespective grooves 752, 753. The flange 741 comprises an arcuate portionin the form of a rib 749 which is disposed radially inwardly of thecompartment 751 and seals this compartment from the remainder of thechamber 730 save for the provision of a relatively narrow clearance orgap 754.

The configuration of surfaces bounding the grooves 752, 753 in the parts731, 732 of the flywheel 703 is preferably such that their curvatureconforms to that of the adjacent portions of coil springs 745 in thecompartment 751. Thus, the radially outermost portions of the coilsprings 745 could come into actual contact with the adjacent portions ofthe surfaces bounding the grooves 752, 753, at least when the apparatus701 rotates so that the coil springs 745 are acted upon by centrifugalforce.

In order to reduce or avoid wear upon the just discussed surfaces of theparts 731 and 732, the apparatus 701 can comprise a band- orstrip-shaped member 781 which is recessed into the part 731 radiallyoutwardly of the compartment 751 and is thus adjacent those portions ofconvolutions of the coil springs 745 which are most likely to rubagainst the flywheel 703 under the action of centrifugal force. Thehardness of the material of the band-like member 781 can greatly exceedthe hardness of the parts 731, 732. The illustrated member 781 is ashort cylinder and is received in a recess 782 of the part 731. Therecess 782 can be formed during casting of the part 731 or it can bemachined into the part 731 in a grinding, milling or other suitablemachine which employs material removing tools. The axial length of themember 781 suffices to ensure that it is contacted by the radiallyoutermost portions of convolutions of the coil springs 745 when theapparatus 701 is in use, i.e., at least while the flywheels 703 and 704rotate with and/or relative to each other.

The parts 731, 732 respectively carry abutments or stops 755, 755a whichextend into the respective grooves 752, 753 and cannot rotate relativeto the flywheel 703. These abutments can be engaged by the endconvolutions of the coil springs 745 in the compartment 751. Each arm744 of the flange 741 is flanked by two abutments 755, 755a. In theembodiment which is shown in FIGS. 11 to 13, the length of the abutments755, 755a in the circumferential direction of the compartment 751 equalsor closely approximates the length of the respective arms 744. FIG. 12shows cup-shaped retainers 759 which are disposed between the arms 744and the adjacent end portions of the respective coil springs 745. Theconfiguration of the retainers 759 is preferably such that they at leastsubstantially fill the corresponding portions of the compartment 751 inorder to offer a substantial resistance to the flow of a viscous fluidmedium along their peripheral surfaces, i.e., between the retainers andthe adjacent portions of surfaces bounding the grooves 752 and 753.

The compartment 751 is disposed radially outwardly of two annularportions 760, 761 of the radially extending surfaces of the parts 731,732, and the portions 760, 761 define a ring-shaped passage 762 which islargely filled by the corresponding portion of the flange 741 so thatthe flange and the part 731 define the aforementioned narrow clearanceor gap 754 providing a path for the flow of fluid medium between thecompartment 751 and the radially inner portions of the chamber 730. Thedistance between the annular portions 760, 761 of radially extendingsurfaces of the parts 731, 732 need not appreciably exceed the thicknessof the corresponding portion of the flange 741, i.e., the flange 741 andthe part 731 can constitute a highly effective flow restrictor whichoffers a pronounced resistance to the flow of fluid medium into and fromthe compartment 751 of the chamber 730.

The compartment 751 accommodates four equidistant coil springs 745 eachof which extends along an arc of or close to 82 degrees. Thus, thecombined length of the four coil springs 745 in the circumferentialdirection approximates 90 percent of a complete circle. As alreadyexplained in connection with the coil springs 45 in the apparatus 1 ofFIGS. 1 and 2, the coil springs 745 are preferably curved prior toinsertion into the compartment 751 because this reduces the internalstresses which develop when the springs 745 are acted upon by theabutments 755, 755a and by the arms 744 in order to store energy.Furthermore, such shaping of the coil springs 745 facilitates theirinstallation in the compartment 751. The initial curvature of the coilsprings 745 can match or merely approximate the curvature of thecompartment 751.

The supply of viscous fluid medium in the chamber 730 is preferably alubricant, and its quantity is preferably selected in such a way that itfills at least the compartment 751 when the apparatus 701 is caused torotate.

As can be seen in FIG. 12, the flange 741 has a central opening 771bounded by a set of radially inwardly extending tooth-like projections772 in mesh with complementary tooth-like projections 773 of the disc727. The projections 772 and 773 together form the aforementionedconnection 742. This connection ensures that the disc 727 and flange 741can be readily separated from each other by moving the flange and/or thedisc axially of the apparatus 701 as well as that, when the apparatus701 is assembled, the flange 741 is compelled to share all angularmovements of the flywheel 704 which carries the disc 727. Theprojections 773 fit into recesses or tooth spaces 772a which alternatewith the projections 772 in the circumferential direction of the surfacebounding the opening 771. The rivets 726 extend through the projections773 of the disc 726 and are anchored in the flywheel 704. As describedin connection with FIGS. 1 and 2, the projections 772, 773 render itpossible to locate the flange 741 in an optimum position between theparts 731, 732 of the housing which defines the chamber 730; this, inturn, renders it possible to keep the width of the clearance or gap 754between the flange 741 and the part 731 to a minimum. The connection 742serves the additional useful purpose of allowing to compensate formachining tolerances of elements which include the flange 741 and theelements adjacent thereto.

The apparatus 701 further comprises a sealing device 774 which preventsor reduces to a minimum the escape of viscous fluid medium radiallyinwardly beyond the innermost portion of the chamber 730. This sealingdevice is installed between the radially innermost portion of the part732 and the flywheel 704. The main difference between the sealing device774 and the sealing device 374 of FIG. 6 is that the entire sealingmember 775 is coated with highly wear-resistant material. The radiallyoutermost portion of the sealing member 775 is held against axialmovement by the portion 732a of the part 732 and by a ring-shapedcarrier 780 which latter is affixed to portion 732a of the part 732 byrivets 732b or similar fasteners.

The portion 732a of the part 732 extends radially inwardly beyond theradially outermost part of the axially resilient sealing member 775 sothat the portion 732a and the member 775 define an annular space 732chaving a wedge-like cross-sectional outline and an open innermostportion of maximum width which is located directly radially outwardly ofthe location of sealing engagement between the radially innermostportion of the member 775 and an insert 776. Such mounting of thesealing member 775 and such configuration of the part 732 ensure thatminute quantities of viscous fluid medium which happen to escape fromthe chamber 730 in the region 776b between the sealing member 775 andinsert 776 gather in the space 732c and are forced back into the chamber730 under the action of centrifugal force when the apparatus 701 is setin rotary motion. As mentioned above, the region 776b of sealingengagement between the insert 776 and the sealing member 775 is locatedradially inwardly of the space 732c and at the same distance from theflange 741, as seen in the axial direction of the flywheels 703 and 704.This ensure that any fluid medium which has managed to pass between theinsert 776 and the sealing member 775 invariably enters the space 732cunder the action of centrifugal force when the flywheels 703, 704 arecaused to rotate at an elevated speed.

The reference character 791 denotes in FIG. 11 a notch which is formedin the part 732 of the housing for the chamber 730 and serves to receivethe radially outermost portion of the sealing member 775 and the carrier780. The notch 791 extends in the axial direction of the flywheel 704from the left-hand side of the part 732 and away from the flange 741.

The radially innermost portion of the part 731 is secured to anextension 720 which is a functional equivalent of the protuberance 20 onthe flywheel 3 of FIG. 1 and is surrounded by the antifriction bearing16 of the bearing means 15. The protuberance 720 has a cylindricalsurface 720b which serves to center the part 731, and acircumferentially extending shoulder 720c which determines the axialposition of the part 731. The manner in which the bearing 16 isinstalled between the flywheels 703 and 704 is or can be the same asdescribed in connection with FIG. 1 or 6. The means for permanently orseparably connecting the part 731 with the protuberance 720 can includea set of screws or rivets, a weld or an upset portion of theprotuberance 720 at the left-hand side of the part 731 (as seen in FIG.11).

The manner of assembling the flywheels 703, 704 of the apparatus 701 isanalogous to the aforedescribed manner of assembling the flywheels 3 and4. of FIGS. 1 and 2. Thus, the antifriction bearing 16 is first mountedin the flywheel 704 and the sealing device 774 is mounted on theflywheel 703. The bearing 16 is thereupon slipped onto the protuberance720 of the flywheel 703 so that the inner race of the bearing surroundsthe cylindrical peripheral surface 720a of the protuberance 720 wherebythe projections 773 of the disc 727 on the flywheel 704 move into meshwith the projections 772 of the flange 741 to establish the connection742. Moreover, the sealing member 775 of the device 774 is stressed inthe axial direction as a result of engagement with the insert 776. Theretaining ring 722 is then affixed to the end face of the protuberance720 to locate the inner race of the bearing 16 in a desired axialposition. This also ensures that the flywheels 703 and 704 aremaintained in predetermined axial positions with reference to eachother. The retaining ring 722 can be riveted, bolted, screwed orotherwise securely affixed to the protuberance 720 of the flywheel 703.

The manner in which the viscous fluid medium which partially fills thechamber 730 performs a desirable hydraulic or viscous damping action isthe same as or similar to that described in connection with FIGS. 1 and2. The damping action is attributable to the establishment of severalflow restrictors as well as to turbulence in the fluid medium.

It is desirable to provide layers of electric insulating materialbetween the parts 731, 732 on the one hand and the adjacent movable orother elements or components of the apparatus 701 on the other hand, atleast for the duration of the welding operation to attach the radiallyoutermost portions of the parts 731, 732 to each other. The absence ofelectric insulating layers could result in partial bonding of movableelements or components of the apparatus 701 (especially of the dampermeans) to the part 731 and/or 732 as well as in an undesirable change oftexture of elements which are sufficiently close to the part 731 and/or732 to be likely to be overheated during making of the welded connection738. The elements which are most likely to be affected by overheatingare the coil springs 745 in the compartment 751 of the chamber 730, thecup-shaped retainers 759 in the compartment 751 and the flange 741.

The layers or coats of insulating material can be provided on the part731, on the part 732 and on the elements or components (such as 741,745, 755, 755a and 759) which are adjacent the parts 731, 732. It is notalways necessary to completely coat the part 731 and/or 732 and/or theelement 741, 745, 755, 755a and/or 759 with electrically insulatingmaterial, i.e., it often suffices to coat the parts 731, 732 only inregions where they contact the aforeenumerated elements and/or to coatthe elements only in regions where they are nearest to the part 731and/or 732. The insulating operation can involve phosphatizing ofmetallic parts. An additional solution is to make certain parts (such asthe cup-shaped retainers 759 and/or the abutments 755, 755a) from anon-conductive material. The springs 745 can be provided with coats oflacquer but the majority of elements which are likely to be affected byoverheating or which are likely to overheat the neighboring elements arepreferably phosphatized. The elements to be phosphatized preferablyinclude the parts 731, 732 (which are made of metallic sheet material)and the flange 741. It is also possible to provide the parts 731, 732and/or the elements or components which are in contact therewith withcoats of suitable ceramic material, plastic material and/or grease. Suchcoats will normally be applied to the parts 731 and 732. It oftensuffices to phosphatize the parts 731, 732 and to merely apply layers oflacquer to the coil springs 745.

In order to simplify the phosphatizing or coating with a layer ofceramic or like material, the corresponding elements or components (suchas the parts 731, 732) are preferably coated in their entirety, and thethus applied coats are thereupon removed in the course of a secondarytreatment in order to expose those portions which are to be welded toeach other as well as those portions which are to be connected with thesource of electrical energy. The secondary treatment can involvemechanical removal of ceramic material, phosphate or the like in amachine tool. This ensures that the parts 731, 732 are electricallyconductive at 738 and at the location or locations of connection to theenergy source. The selection of insulating material should be made witha view to ensure that the selected material is compatible with viscousfluid medium which is thereupon admitted into the chamber 730 to fill atleast the compartment 751.

It is further preferred to select the insulating layer or layers(especially phosphatized coats) in such a way that they exhibit highlysatisfactory wear resistant and self-lubricating properties.

The periphery of the part 731 defines a cylindrical seat 739 for thestarter gear 740. The latter is preferably welded, as at 740a, to thepart 731. The welded connection can be established all the way aroundthe part 731 or it can consist of several spot welds. A connection whichinvolves welding is preferred at this time in view of the limitedthickness of the metallic sheet material which is used for the making ofthe part 731. As can be seen in FIG. 11, the axial length (thickness) ofthe gear 740 is greater than the thickness of the material of the part731. FIG. 11 further shows that the thickness of the part 731 exceedsthe thickness of the part 732.

Referring to FIG. 13, the abutments or stops 755, 755a of the apparatusof FIGS. 11 and 12 can be replaced with pocket-like abutments 755c, 755dwhich are integral portions of the respective parts 731 and 732. Thissimplifies the making and assembly of the respective apparatus becausethe number of separately produced parts is reduced and the abutments areinvariably located in optimum positions for engagement with the endportions of the adjacent coil springs. The recesses which are formed inthe outer sides of the parts 731, 732 shown in FIG. 13 as a result ofthe making of pockets 755c, 755d can be used for reception of centeringdevices (not shown) which ensure that the parts 731,732 are properlycentered and otherwise positioned relative to each other in the courseof the welding operation. The centering devices are normally provided inor on the welding apparatus which is used to connect the parts 731, 732to each other, i.e., to form the welded connection 738 shown in FIG. 11.The dimensions of the centering devices are preferably selected with aview to ensure that such devices fill or practically fill the recessesat the outer sides of the pockets which constitute the abutments 755cand 755d of FIG. 13. Such centering devices can constitute electrodeswhich supply the welding current and/or the means for pressing the parts731, 732 against each other in the course of the welding operation. Itis particularly advantageous if the centering devices are constructed,configurated and mounted in the welding apparatus in such a way thatthey are invariably located at a predetermined distance from each other(i.e., that the centering devices which enter the recesses outside ofthe pcokets 755c and 755d are located at a preselected axial distancefrom one another); this ensures that the parts 731, 732 are located atan optimum axial distance from one another when the welding operation iscompleted. This is important in view of the aforediscussed need forproper dimensioning of the compartment 751 (to avoid excessive orinsufficient rubbing contact between the surfaces surrounding thegrooves 752, 753 on the one hand and the surfaces of convolutions of thecoil springs 745 on the other hand). Moreover, proper positioning of theparts 731, 732 is important in view of the aforediscussed need to ensurethat the elements defining the gap 754 will constitute effective flowrestrictors by offering an optimum resistance to the flow of viscousfluid medium into and from the compartment 751.

The apparatus 801 of FIGS. 14 and 15 comprises a composite flywheel 802which includes a first component or flywheel 803 secured to the outputelement 805 (e.g., a crankshaft) of the internal combustion engine by aset of bolts 806 or analogous fasteners, and a second component orflywheel 804 which can be connected with the input element 810 of achange-speed transmission in response to engagement of a friction clutch807. The clutch 807 includes a cover 811 which is affixed to theflywheel 804, an axially movable pressure plate 808 between the cover811 and the flywheel 804, a clutch plate or clutch disc 809 having a hubwhich is non-rotatably mounted on the input element 810 of thetransmission and a set of friction linings which are disposed betweenthe pressure plate 808 and the friction surface 804a of the flywheel804, and a diaphragm spring 812 which is tiltable between two seats atthe inner side of the cover 811 and biases the pressure plate 808against the adjacent friction lining of the clutch plate 809 when theclutch 807 is engaged. The pressure plate 808 is axially movably butnon-rotatably coupled to the cover 811 and/or to the flywheel 804. Themeans for engaging or disengaging the clutch 807 is of conventionaldesign and is not shown in the drawing.

The damper means between the flywheels 803 and 804 includes a first orouter damper 813 and a second or inner damper 814. The dampers 813, 814are connected in parallel and each thereof is designed to yieldablyoppose rotation of the flywheels 803, 804 relative to each other.

The bearing means 815 between the flywheels 803, 804 comprises anantifriction ball bearing 816 with a single annulus of rolling elementsbetween an inner race 819 and an outer race 817. The outer race 817 isinstalled in an axial recess 818 of the flywheel 804, and the inner race819 surrounds a cylindrical portion of the peripheral surface of anaxial protuberance 820 forming part of the flywheel 803. Theprotuberance 820 extends axially in a direction away from the outputelement 805 of the engine and is received in the recess 818 of theflywheel 804; this protuberance is integral with a radially outwardlyextending flange 803a of the flywheel 803.

The inner race 819 is preferably a press fit on the protuberance 820 andabuts a circumferential shoulder 821 of the protuberance under theaction of a washer-like retaining ring 822 which is secured to theprotuberance by the heads of the aforementioned bolts 806. The bearing816 is held against axial movement with reference to the flywheel 804 bybeing fixed between a disc 827 which is secured to the flywheel 804 by aset of distancing elements in the form of rivets 826 and by abutting aninternal shoulder 825 in the recess 818. The outer race 817 of thebearing 816 is flanked by two rings 823, 824 each of which has anL-shaped cross-sectional outline and which constitute a thermal barrierbetween the friction clutch 807 and the bearing 816, and moreparticularly between the friction surface 804a and clutch plate 809 onthe one hand and the races 817, 819 and rolling elements of the bearing816 on the other hand.

The radially extending flange 803a of the flywheel 803 is integral witha cylindrical collar 828 which surrounds the radially outermost portionof an annular chamber 829. The collar 828 extends in the axial directionof the apparatus 801 and forms part of the housing for the chamber 829;such housing further includes two radially extending sections or parts831, 832 which flank the dampers 813 and 814. The part 831 is anintegral portion (833) of the radially extending flange 803a of theflywheel 803, i.e., of the element which is integral with and extendsradially outwardly from the protuberance 820. The part 832 is asubstantially or completely non-elastic rigid disc-shaped member whichis disposed between the part 831 and the flywheel 804 and can be said toconstitute a radially extending cover of the housing for the chamber829. The radially outermost portion of the part 832 abuts the end faceof the collar 828 and is secured to the latter by a set of rivets 834 oranalogous fastener means.

The dampers 813, 814 comprise a common output element 835 which isnon-rotatably connected to the flywheel 804. The output element 835includes the aforementioned disc 827 which is affixed to the end face ofa protuberance or projection 836 which surrounds the recess 818 andforms an integral part of the flywheel 804. The projection 836 extendsaxially toward the output element 805 of the engine. The output element835 further includes a second disc 837 which is secured to the disc 827.FIG. 14 shows that the radially outermost portion of the disc 827 isdished or cupped in a direction toward the flange 803a of the flywheel803 and that the disc 837 is affixed to the radially outermost (cuppedor dished) portion 837a of the disc 827 by a set of rivets 838.

The dished or cupped configuration of the radially outermost portion ofthe disc 827 results in the formation of a recess or space 839 which isdisposed between the discs 827, 837 and receives a disc-shaped member orflange 840 constituting the input element of the inner damper 814. Thediscs 827, 837 have registering openings or windows 841, 842 whichregister with windows 843 in the flange 840 and serve to receive energystoring elements in the form of coil springs 844 forming part of theinner damper 814. The length of the windows 841, 842 (as seen in thecircumferential direction of the flywheels 803 and 804) equals orclosely approximates the length of the windows 843, and each coil spring844 is installed in the respective set of windows 841-843 in prestressedcondition. This ensures that a certain moment can be transmitted betweenthe input element or flange 840 of the inner damper 814 and the outputelement 835 of the outer damper 813 before the coil springs 844 undergofurther compression.

The disc 837 (forming part of the output element 835), which is nearerto portion 833 of the flywheel 803 than the other disc 827, has an innerdiameter (at 845) which exceeds the inner diameter of the disc 827. Thelatter cooperates with the shoulder 821 of the protuberance 820 to fixthe bearing 816 in an optimum axial position. FIG. 15 shows that theradially innermost portion of the input element 840 of the damper 814 isprovided with radially inwardly extending tooth-like projections 846which mate with projections 847 on the portion 833 of flywheel 803. Theprojections 847 are rivets which are secured to the portion 833 of theflywheel 803 and each of which includes a portion (head) 847a extendingaxially beyond the general plane of the portion 833 and toward theflywheel 804 (see FIG. 14). The projections 846 cooperate with theprojections 847 to limit the extent of angular movability of the inputelement 840 of the damper 814 with reference to the flywheel 803.

FIG. 15 further shows that the input element 840 of the inner damper 814can turn relative to the flywheel 803 in the driving direction 848 (whenthe engine drives the input element 810 of the change-speedtransmission) through a first angle 849 (before the heads 847a of therivets 847 are engaged by the adjacent projections 846 of the inputelement 840) and that the input element 840 can turn with reference tothe flywheel 803 through a second angle 851 in the opposite direction850 (when the vehicle embodying the power train which employs theapparatus 801 is coasting). In the embodiment of FIGS. 14 and 15, theangle 849 equals or closely approximates the angle 851. However, it isalso possible to select a non-symmetrical positioning of the rivets 847with reference to the projections 846 of the input element 840 so thatthe angle 849 deviates from the angle 851. For example, the angle 849could exceed the angle 851.

The cupped or dished radially outermost portion 837a of the disc 827need not be a circumferentially complete member; as shown in FIG. 15,the portion 837a consists of several radially outwardly extending armseach of which has a bend at its radially innermost end. The disc 837comprises radially outwardly extending prongs or lugs 852 each of whichis adjacent an arm (837a) of the disc 827 and is secured thereto by arivet 838. The length of the lugs 852 in the circumferential directionof the discs 827, 837 is the same as that of the arms 837a, and each arm837a is in register with a lug 852. This renders it possible to use thecoplanar edge faces of the lugs 852 and arms 837a as abutments or stops853, 854 for the coil springs 855 of the outer damper 813.

The discs 827, 837 are further connected to each other by distancingelements in the form of rivets 856 which are disposed at the level ofcoil springs 844 in the inner damper 814, i.e., the annulus of rivets856 has the same radius as the annulus of coil springs 844. Portions ofthe rivets 856 extend with play (as seen in the circumferentialdirection of the flywheels 803 and 804) through apertures or slots 857of the disc-shaped input element 840. The dimensions of the slots 857are selected in such a way that the coil springs 844 of the inner damper814 are fully compressed (i.e., that each spring 844 acts not unlike arigid block because its convolutions lie flush against each other)before the rivets 856 come into engagement with surfaces at the ends ofthe respective slots 857. Such dimensioning of the slots 857 ispreferred at this time because it ensures that abrupt shocks whichdevelop during transmission of torque between the flywheels 803 and 804do not entail the development of pronounced impacts. This is due to thefact that, prior to undergoing total compression (to act not unlikesolid blocks), the coil springs 844 exhibit a very pronouncedprogressivity of their characteristics. This takes place while thesprings 844 are still capable of performing a certain axial movement asa result of radial shifting.

FIG. 15 shows that the rivets 856 are located radially inwardly of thearms 837a and lugs 852. The disc-shaped input element 840 has cutouts858 which are located radially inwardly of the lugs 852, arms 837a andslots 857, and the cutouts 858 are flanked by the arms 846. The cutouts858 are provided to facilitate deformation of the rivets 826 which aredisposed at the same distance from the axis of the composite flywheel802 and whose heads are in register with the cutouts 858.

The input element 840 of the inner damper 814 is clamped axially betweenthe discs 827, 837 which constitute the output element 835 of the outerdamper 813. To this end, the input element 840 constitutes a diaphragmspring which is resilient in the axial direction and exhibits a certainamount of conicity prior to mounting between the discs 827, 837. Whenproperly installed, the input element 840 is stressed axially so that afriction lining or pad 859 between the radially outermost portion of theelement 840 and the disc 837 is compressed as well as that a frictionlining or pad 860 between the radially innermost portion of the element840 and the disc 827 is also kept in compressed condition. In order tofacilitate assembly of the apparatus 801, the friction pads 859 and 860are preferably bonded to the respective sides of the input element 840.The friction pad 859 is disposed radially outwardly and the friction pad860 is located radially inwardly of coil springs 844 in the inner damper814. When the input element 840 of the inner damper 814 turns relativeto the output element 835 of the outer damper 813, the friction pads859, 860 produce a frictional damping action which is effective inparallel to the bias of the coil springs 844.

The parts 831 and 832 of the housing for the chamber 829 are providedwith arcuate grooves 861, 862 which together form the major part of acompartment for the coil springs 855 of the outer damper 813. Thesegrooves receive (either entirely or in part) those portions 6f the coilsprings 855 which extend beyond the respective sides of the outputelement 835. FIG. 14 shows that the curvature of the surfaces boundingthe grooves 861, 862 equals or approximates the curvature of the coilsprings 855, at least in those regions which receive the radiallyoutermost portions of convolutions of the springs 855. This enables theconvolutions of the coil springs 855 to actually contact and be guidedby the adjacent portions of surfaces bounding the grooves 861, 862, atleast when the apparatus 801 is rotated and the coil springs 855 areacted upon by centrifugal force. It has been found that suchconfiguration of the surfaces bounding the grooves 861, 862 entails apronounced reduction of wear because wear between the convolutions ofthe coil springs 855 and the parts 831, 832 is not localized but takesplace between relatively large portions of abutting surfaces on 831, 832on the one hand and 855 on the other hand. Each of the grooves 861, 862is a circumferentially complete recess in the respective part 831, 832.This is desirable and advantageous because the grooves 861, 862 can beformed during casting of the respective parts 831, 832 and the surfacesbounding such grooves can be thereupon treated to a desired degree offinish in a suitable machine using grinding, milling or other materialremoving tools.

The grooves 861, 862 respectively contain abutments or stops 863, 864which engage the end convolutions of the adjacent coil springs 855. Thelength of the abutments 863, 864 in the circumferential direction of theflywheel 803 is the same as that of the arms 837a on the disc 827 and ofthe lugs 852 on the disc 837. Each of the abutments 863, 864 canconstitute a separately produced element which fits rather snugly intothe corresponding portion of the respective groove 861, 862 and isriveted or otherwise reliably secured to the respective part 831, 832.The end portions of the abutments 863 and 864 are preferably flattenedto ensure the establishment of large-area contact with the endconvolutions of the adjacent coil springs 855.

FIG. 15 shows that the outer damper 813 comprises three coil springs 855each of which extends along an arc of approximately 110 degrees.

The relationship between the parameters of coil springs 844 and 855 isselected in such a way that, when the angular displacement of theflywheels 803, 804 reaches a maximum value, the final or maximum momentwhich is furnished by the outer coil springs 855 is less than thecorresponding moment which is furnished by the inner coil springs 844.Furthermore, the spring rate of the inner springs 844 is greater thanthat of the outer springs 855.

The means for sealing the radially outermost portion of the chamber 829for the dampers 813, 814 from the surrounding atmosphere comprises asealing ring 865 which is mounted between the cylindrical collar 828 ofthe flywheel 803 and the part 832 radially inwardly of the rivets 834.The illustrated sealing ring 834 can constitute a simple O-ring.

A sealing device 866 is installed between the radially innermost portionof the part 832 and the axial projection 836 of the flywheel 804 to sealthe radially innermost portion of the chamber 829 from the atmosphere.The sealing device 866 includes a ring-shaped member which has adisc-shaped inner portion clamped between the projection 836 of theflywheel 804 and the disc 827, and a frustoconical outer portion whichacts not unlike a diaphragm spring and engages, in axially stressedcondition, the adjacent portion of the part 832. Such frustoconicalouter portion of the sealing device 866 is received in a radiallyoutwardly extending ring-shaped notch 867 of the part 832 at that sideof this part which faces the disc 827. The surface bounding the notch867 surrounds the sealing device 866 and extends along one side of thefrustoconical outer portion of 866.

The chamber 829 contains a supply of viscous fluid medium which ispreferably a lubricant. When the apparatus 801 is rotated, the fluidmedium fills the outermost portion of the chamber 829 and preferablyextends radially inwardly at least to the level of the axes of coilsprings 855 forming part of the outer damper 813.

A radially extending ventilating or aerating channel 868 is providedbetween the part 832 and the flywheel 804 to ensure adequate cooling ofthe fluid medium in the chamber 829. The radially outermost portion ofthe channel 868 is open and the radially innermost portion of thischannel communicates with substantially axially extending passages 869which are provided in the flywheel 804 radially inwardly of the frictionsurface 804a.

The rivets 834 can be used as a means for locating the starter gear 890in a predetermined axial position with reference to the flywheel 803.

The apparatus 801 operates as follows:

When one of the flywheels 803, 804 leaves the idle position of FIG. 15,e.g., in the coasting direction 850, the coil springs 855 of the outerdamper 813 are caused to store energy. When the one flywheel (e.g., theflywheel 804) completes the angle 851, the radially inwardly extendingprojections 846 of the input element 840 of the inner damper 814 engagethe respective abutments 847 of the flywheel 803 so that any furtherangular displacement of the flywheel 804 in the direction 850 thenentails joint compression of coil springs 855 and 844. Such jointcompression of coil springs 844 and 855 continues until the coil springs844 begin to act not unlike solid blocks, i.e., when the convolutions ofthe coil springs 844 are immediately adjacent to and abut each other.This terminates the angular displacement of the flywheel 804 relative tothe flywheel 803. In the embodiment of FIGS. 14 and 15, the angle 851equals or approximates 32 degrees and the so-called blocking angle ofthe coil springs 844 is approximately 4 degrees so that the totalangular displacement of the flywheel 804 relative to the flywheel 803(and/or vice versa) can be in the range of 36 degrees. A frictionaldamping action takes place while the coil springs 844 store energybecause the friction pads 859, 860 on the input element 840 15respectively rub along the discs 827, 837. Additional frictional dampingaction is generated as a result of sliding contact between theconvolutions of the coil springs 855 and the adjacent portions ofsurfaces bounding the grooves 861, 862 in the parts 831, 832. Moreover,the radially outermost portion of the sealing device 866 slides alongthe part 832 to generate additional frictional damping action. The fluidmedium in the chamber 829 is agitated as well as displaced from thecompartment for the coil springs 844, and this results in thedevelopment of hydraulic or viscous damping action in a manner and forreasons as explained above in connection with the apparatus 1 of FIGS. 1and 2.

FIG. 16 shows a portion of an apparatus 901 having a flange 941 whichhas radially outwardly extending abutments or arms 944. (one shown).These arms serve to compress energy storing elements in the form of coilsprings 945, 945a of a damper 913 in a manner as described in connectionwith the apparatus shown in FIGS. 1 through 15. The coil springs 945,945a are confined in an annular compartment 951 forming part of achamber between the parts of the flywheel 903. The coil spring 945a isbiased directly by the adjacent abutment or arm 944 and the coil spring945a is acted upon by a cup-shaped retainer 959. Each arm 944 has twoprojections in the form of stubs or noses 944a, 944b which extend inopposite directions (i.e., away from each other) in the circumferentialdirection of the flywheel 903. The illustrated cup-shaped retainer 959has a conical or spherical socket 959a in the form of a blind bore forthe stub 944a of the arm 944. The configuration of the stub 944a is suchthat it can hold the retainer 959 and hence the adjacent hollow endportion of the coil spring 945 in a position such that the end portionof the coil spring is out of contact with the adjacent radiallyinnermost or outermost portion of the compartment 951 at least when thespring 945 is caused to store energy. To this end, the stub 944a has asloping ramp-like cam face 944c along which the adjacent portion 959b ofthe internal surface of the retainer 959 slides when the retainerapproaches the main portion of the arm 944 whereby the inner part of therespective end portion of the coil spring 945 is lifted off or urgedtoward the adjacent surface bounding the compartment 951, i.e., such endportion of the coil spring 945 is moved radially outwardly or inwardly.The retainer 959 and its socket 959a have a circular cross-sectionaloutline.

The other stub 944b of the arm 944 which is shown in FIG. 16 has a camface or ramp 944d which is adjacent the innermost portion of thecompartment 951 and cooperates with the end convolution of the coilspring 945a to urge such end convolution radially inwardly, i.e., towardthe adjacent portion of the surface bounding the compartment 951.

If the apparatus 901 employs cup-shaped retainers 959, it is advisableto ensure that the outline of the stub 944a (or at least the outline ofthe ramp 944c) conforms to the outline of the adjacent portion 959b ofthe internal surface of the retainer 959; this ensures that the adjacentend convolutions of the coil spring 945 are pulled radially inwardlyeven if the angular position of the retainer 959 with reference to thearm 944 and its stub changes.

Projections corresponding to the stubs 944a, 944b shown in FIG. 16 canbe used with equal or similar advantage in apparatus which are shown inFIGS. 1 to 15. Moreover, such projections or stubs can be provided onthe aforediscussed abutments or stops in the compartments of chambers 30. . . 829 of the previously described apparatus.

An advantage of the stubs 944a, 944b is that they can maintain theadjacent convolutions of the coil springs 945, 945a out of contact withthe radially outermost portions of surfaces bounding the compartment 951even if the flywheel 903 is rotated at a very high speed. Consequently,the axial length of the coil springs 945, 945a can be readily changedbecause they cause a minimum of frictional damping. An additionaladvantage of the stubs 944a, 944b is that they enable the adjacent endconvolutions of the coil springs 945, 945a to move in the compartment951 (i.e., to move toward or away from the arm 944) even if thefrictional engagement between the median convolutions of such coilsprings and the surfaces bounding the compartment 951 is very high,i.e., even if such median convolutions are prevented from sliding in thecircumferential direction of the flywheel 903. This can take place whenthe rotational speed of the flywheel 903 is very high so that the medianconvolutions of the springs 945, 945a are acted upon by a very largecentrifugal force. The freely slidable end convolutions of the coilsprings 945, 945a are then still capable of damping high-frequencylow-amplitude oscillations and similar stray movements of the flywheels.

The flange 941 is normally a flat stamping. The projections 944a, 944bof its arms 944 can receive a cylindrical, frustoconical or partlycylindrical or partly frustoconical shape as a result of secondarytreatment in a suitable deforming machine. This enlarges the area ofcontact between the projections 944a and the internal surfaces of therespective cup-shaped retainers 959 on the one hand, and between theprojections 944b and the hollow end portions of the respective coilsprings 945a on the other hand. As mentioned above, the sockets 959a ofthe retainers 959 can have a conical, frustoconical or sphericaloutline.

The provision of projections 944a and/or 944b (i.e., of means forkeeping at least the end portions of the coil springs 945 and/or 945aout of contact with the surfaces bounding the radially outermost portionof the compartment 951) is desirable and advantageous in many or mostinstances. However, certain apparatus are preferably designed in such away that the movements of convolutions of the coil springs intofrictional engagement with the adjacent outermost portions of surfacesbounding the compartment 951 (and/or the compartment for the coilsprings of the inner damper) is promoted, at least when the flywheelsrotate and the coil springs are acted upon by centrifugal force. This isdesirable in apparatus wherein the coil springs begin to store energyonly after a certain initial angular displacement of the flywheelsrelative to each other.

Referring to FIG. 17, there is shown a portion of an apparatus 1001which has a composite flywheel including a first flywheel 1003 and asecond flywheel 1004. The flywheel 1003 is connected to the outputelement of the engine (not shown), and the flywheel 1004 can beconnected to a change-speed transmission by way of a friction clutch,not shown, in the same way as described in connection with FIGS. 1 and2. The flywheel 1003 comprises two sections or parts 1031, 1032 whichare made of deformable metallic sheet material and define an annularchamber 1030 for two series-connected dampers 1013, 1014. The coilsprings of the dampers 1013, 1014 are coupled to each other by a flange1041. The latter is flanked by two discs 1065, 1066 in a mannersubstantially as described in connection with FIG. 10.

The difference between the flange 1041 of FIG. 17 and the previouslydescribed similarly referenced flanges is that the radially outwardlylocated arms 1044 which extend into the compartment 1051 of the chamber1030 have extensions 1044a which are disposed radially outwardly of therespective coil springs 1045 of the damper 1013. Thus, the radiallyoutermost portions of convolutions of the coil springs 1045 can abut theinner sides of the adjacent extensions 1044a, at least when theflywheels 1003, 1004 rotate and the convolutions of the coil springs1045 are acted upon by centrifugal force. It is rather simple to hardenselected portions of or the entire flange 1041 so that it can standextensive wear in spite of repeated and extensive frictional engagementwith the coil springs 1045 of the damper 1013. For example, theextensions 1044a (and, if necessary, certain other portions) of theflange 1041 can be treated by induction hardening. Moreover, and if itis more convenient or less expensive, at least the extensions 1044a ofthe flange 1041 can be coated with layers of highly wear resistantmaterial such as solid or hard nickel or the like.

The extensions 1044a of arms 1044 forming part of the flange 1041 arereceived in the radially outermost portion 1051a of the compartment1051. The portion 1051a is also defined by the parts 1031, 1032 of theflywheel 1003; these parts include frictional engagement reducinginserts or portions 1031a, 1032a which extend radially outwardly beyondthe outermost portion 101a of the compartment 1051. The portions 1031a,1032a also extend in the axial direction of the apparatus 1001 so thatthey form a sleeve or shell around the adjacent part of the radiallyoutermost portion of the flywheel 1004. The portions 1031a, 1032a arewelded to each other, as at 1038, preferably in the region of theirrightmost ends as seen in FIG. 17. Such operation can be carried out inan electron beam welding machine. An advantage of the portions 1031a,1032a is that they increase the moment of inertia of the flywheel 1003without it being necessary to unduly enlarge the apparatus 1001 in theradial direction.

That side of the part 1031 of the flywheel 1003 which faces toward theengine is adjacent a disc 1090 which can be said to constitute a scalewith graduations or other forms of indicia 1091 (e.g., projections,notches or the like) which are indicative of different parameters of theengine, for example, the timing of ignition and/or others. Reference maybe had to commonly owned U.S. Pat. No. 4,493,409.

The flywheel 1003 further includes a centrally located axialprotuberance 1020 which extends in a direction away from the outputelement of the engine and is secured to the scale 1090 and part 1031 bybolts, screws or other suitable fasteners 1092. The protuberance 1020 issurrounded by an antifriction ball bearing 1016 on which the flywheel1004 can rotate relative to the flywheel 1003 and/or vice versa.

The utilization of aforediscussed radially outermost portions 1031a,1032a is not limited to those apparatus wherein the parts of the housingfor the annular chamber which confines the dampers are made ofdeformable metallic sheet material. It is also possible to rely on suchmode of shaping the radially outermost portion of the flywheel which isattached to the output element of the engine in apparatus wherein theparts of the housing are castings.

The apparatus 1101 of FIG. 18 comprises a housing which defines anannular chamber (including an annular compartment 1151) and includes twoparts or sections 1131a, 1132a which are made of deformable metallicsheet material. The compartment 1151 serves to receive energy storingcoil springs 1145 forming part of a damper in the chamber. The parts1131a, 1132a further define a radially extending ring-shaped passage1162 which is located radially inwardly of and communicates with thecompartment 1151 and is substantially filled by the respective portionof the flange 1141. Those portions (1165, 1166) of the parts 1131a,1132a which extend radially inwardly beyond the passage 1162 areconnected with thicker parts 1131, 1132 by means of rivets 1155, 1155aor the like. It can be said that each section of the housing for thechamber which includes the compartment 1151 includes two layers orstrata including an outer layer 113, 1132 and an inner layer 1131a,1132a.

The portions 1165, 1166 of the parts 1131a, 1132a can extend radiallyinwardly beyond the respective rivets 1155, 1155a to define a secondannular compartment (not shown) for the coil springs of a second orinner damper corresponding to the damper 14 of the apparatus 1 shown inFIGS. 1 and 2. Alternatively, the portions 1165, 1166 need not extendradially inwardly well beyond the rivets 1155, 1155a; instead, suchportions can define arcuate compartments for the coil springs of asecond or inner damper between neighboring pairs of rivets 1155, 1155aas seen in the circumferential direction of the flywheel including theparts 1131, 1132, 1131a, 1132a.

The radially outermost portions of the parts 1131, 1132 are connected toeach other radially outwardly of the compartment 1151 and of the parts1131a, 1132a. The connection includes suitably bent prongs 1133 whichconstitute relatively thin extensions of the part 1132 and overlieradially outwardly extending lugs 1134 of the part 1131. The lugs 1134can form a circumferentially complete rib or bead around the remainingportion of the part 1131. Pins 1138 are used to couple the extensions1133 to the lugs 1134 so as to hold the parts 1131, 1132 against angularmovement relative to each other.

The utilization of housings with inner and outer sections or partscorresponding to the parts 1131, 1131a and 1132, 1132a of FIG. 18 is notlimited to the apparatus 1101 (wherein each of the parts 113, 1131a,1132, 1132a is made of deformable metallic sheet material) but can beused with equal or similar advantage in apparatus wherein each part orsection of the housing includes a casting. If one part is a casting, itis provided with a suitable recess which accommodates the inner part(corresponding to the part 1131a or 1132a). The arrangement may be suchthat the recesses of the castings accommodate at least those portions ofthe inner parts 1131a, 1132a which surround the energy storing elementsof the respective damper or dampers.

The apparatus 1201 of FIG. 19 has two flywheels one of which comprises ahousing for an annular chamber 1230. The housing includes two parts1231, 1232 which flank a flange 1241 extending in part into an annularcompartment which forms the radially outermost portion of the chamber1230 and receives the coil springs of a damper 1213. The chamber 1230 isat least partially filled with a viscous fluid medium, preferably alubricant. The flange 1241 is fixedly secured to an axial protuberanceor projection 1243 of the flywheel 1204 by a set of distancing elementsin the form of rivets (only one shown). A sealing device 1274 isprovided between the flange 1241 and the part 1232 of the housing forthe chamber 1230.

The apparatus 1201 further comprises a dry friction generating device1290 which is located radially inwardly of the part 1232 (i.e., outsideof the chamber 1230) and is installed between the flange 1241 and theradially extending flange-like portion 1204a of the flywheel 1204. Thefriction generating device 1290 comprises a friction disc 1294 which isflanked by friction pads 1294a, 1294b. The pad 1294a is mounted betweenthe friction disc 1294 and the flange 1241 and the pad 1249b is biasedby a biasing device 1293 in the form of a washer which is acted upon bya diaphragm spring 1292. The spring 1292 is installed in prestressedcondition between the radial portion 1204a of the flywheel 1204 and thebiasing device 1293.

The friction disc 1294 is provided with radially outwardly extendingarms 1295 which mate with radially inwardly extending projections orprongs 1295a of the part 1232. The arrangement is or can be such thatthe arms 1295 and the prongs 1295a mate without any play (as seen in thecircumferential direction of the flywheels) or with a selected play,i.e., the friction disc 1294 and the part 1232 can have a certainfreedom of angular movement relative to each other. Thus, the frictiongenerating device 1290 can become effective only after at least one coilspring of the damper 1213 begins to store energy as a result of angulardisplacement of at least one flywheel relative to the other flywheel.

The apparatus 1301 of FIG. 20 comprises a damper 1313 in a compartment1351 which is outwardly adjacent two sealing devices 1374, 1374acooperating with the adjacent portion of the flange 1341. The sealingdevice 1374 acts between the flange 1341 and the part 1332 of thehousing for the annular chamber which includes the compartment 1351, andthe sealing device 1374a acts between the flange 1341 and the part 1331.

That portion of the flange 1341 which is disposed radially inwardly ofthe sealing devices 1374, 1374a is flanked by and maintained in contactwith two friction pads 1394a, 1394b which, in turn, are flanked by discs1393, 1394. The disc 1394 is fixedly secured to the flywheel 1304 bydistancing elements in the form of rivets 1367. The other disc 1393 ismovable axially of the apparatus 1301 and is biased axially toward thefriction pad 1394b by a diaphragm spring 1392 which reacts against theradially extending portion or flange 1304a of the flywheel 1304. Thediaphragm spring 1392 and the disc 1393 have cutouts in the form ofopenings, slots or windows for the respective portions of the distancingelements 1367 so as to ensure that the spring 1392 and the disc 1393 arecompelled to share the angular movements of the flywheel 1304.

The bias of the prestressed diaphragm spring 1392 determines the momentwhich is required to turn the flange 1341 relative to the flywheel 1304,i.e., the spring 1392 determines that force which is required to causethe flange 1341 to slip with reference to the flywheel 1304. It can besaid that the radially innermost portions of the flange 1341 and theelements 1392 to 1394b jointly form a force-locking clutch or slipclutch 1390 in series with the damper 1313. The damping action of theclutch 1390 increases with increasing angular displacement of theflywheels relative to each other.

In order to limit the extent of angular movability of the flange 1341relative to the flywheel 1304, the radially innermost portion of theflange 1341 can be provided with projections which alternate with thedistancing elements 1367 (as seen in the circumferential direction ofthe flywheel 1304). Such projections then cooperate with the shanks ofthe distancing elements 1367 to determine the extent of angularmovability of the flywheel 1304 and the flange 1341 relative to eachother. The just discussed projections of the flange 1341 are optional,i.e., it is possible to mount the flange 1341 in such a way that, when acertain force is exerted, the flange has unlimited freedom of angularmovement relative to the flywheel 1304. In such apparatus, the slipclutch 1390 is designed in such a way that the moment which can betransmitted thereby exceeds the nominal torque of the engine whichdrives the flywheel including the parts 1331, 1332.

In accordance with a modification which is not specifically shown in thedrawing, the apparatus 1301 of FIG. 20 can be constructed in such a waythat the flange 1341 is mounted with limited freedom of angular movementrelative to the flywheel 1304 and the apparatus comprises a seconddamper having energy storing elements in the form of coil springs whichare installed in windows provided therefor in the discs 1393, 1394 andflange 1341. The windows for such additional coil springs are providedin the discs 1393, 1394 and flange 1341 between neighboring distancingelements 1367 as seen in the circumferential direction of the flywheel1304. It is then advisable to ensure that the spring rate of additionalcoil springs (which are installed in the region of the slip clutch 1390)be much higher than that of coil springs forming part of the damper1313. Moreover, the frictional damping action which is generated by theslip clutch 1390 should be much more pronounced than the frictionaldamping action of the damper 1313 (while this damper is active) andwhich is produced, among others, by the sealing devices 1374, 1374a incooperation with the flange 1341.

The apparatus 1401 of FIG. 21 comprises three dampers 1413, 1413a, 1414which operate in parallel. The sections or parts 1431, 1432 of thehousing for the annular chamber 1430 which accommodates the dampersdefine two annular compartments 1451, 1451a which respectively receivethe coil springs of the dampers 1413 and 1413a. The coil springs of thedampers can be deformed by the prongs or arms of a flange 1441 which isinstalled between the parts 1431, 143a.

The parts 1431, 1432 define a third annular compartment or space 1452which receives the coil springs of the innermost damper 1414. To thisend, the parts 1431, 1432 have arcuate grooves at the respective sidesof the flange 1441. The radially innermost portion of the compartment orspace 1452 is substantially open. The quantity of viscous fluid mediumin the chamber 1430 is selected in such a way that the fluid mediumfills at least the outermost compartment 1451 but preferably the twooutermost compartments 1451, 1451a.

The hydraulic or viscous damping action of the damper 1413 can deviatefrom the damping action of the damper 1413a. The damping action of eachof the dampers 1413, 1413a can be varied in a number of ways,particularly by appropriate selection of the clearance or gap betweenthe flange portion 1441a and the adjacent portions of the parts 1431,1432 intermediate the compartments 1451, 1451a and/or of the clearanceor gap between the flange portion 1441b and the parts 1431, 1432radially inwardly of the compartment 1451a. Such regulation of thehydraulic damping action of the damper 1413 and/or 1413a can be reliedupon in order to conform the apparatus 1401 for use in a particularpower train. Furthermore, the hydraulic damping action can be varied inthe previously described manner by appropriate selection of flowrestrictors including cup-shaped retainers for coil springs in thecompartment 1451 and/or 1451a. One or two cup-shaped retainers can beprovided for one, two or more coil springs in the compartment 1451and/or 1451a. The same applies for regulation of the damping action ofthe innermost damper 1414.

The apparatus 1401 can be modified by increasing the number ofconcentric dampers to four or even more. Furthermore, the dampers 1413,1413a and 1414 can be connected in series rather than in parallel. It isalso possible to provide a connection in parallel between two or thesedampers and a series connection between another pair of these dampers.

FIG. 21 shows a portion of an apparatus 1501 wherein two dampers 1513,1513a are disposed side by side, i.e., at the same or at nearly the sameradial distance from the axes of the flywheels. The output elements ofthe dampers 1513, 1513a include two flanges 1541, 1541a having dished orcupped radially outermost portions in the respective compartments 1551,1551a. The inner portions of the flanges 1441, 1441a are adjacent oneanother and are attached to the section or part 1532 of the housing forthe chamber which includes the compartments 1551, 1551a by distancingelements in the form of rivets 1565. The sections or parts 1531, 1532are elements of the flywheel 1503 which is affixed to the output element(not shown) of the internal combustion engine.

The radially innermost portions of the compartments 1551, 1551a areopen; these compartments respectively receive the coil springs of thedampers 1513, 1513a. At least the major portions of surfaces boundingthe compartments 1551, 1551a and provided on the parts 1531, 1532 of thehousing for the annular chamber which includes these compartments areconfigurated in such a way that their curvature conforms to that of coilsprings forming part of the respective dampers 1513, 1513a.

The coil springs of the dampers 1513, 1513a can be designed and mountedin such a way that they undergo compression one after the other, eitherindividually or in groups of two or more. This renders it possible toimpart to the damper means including the dampers 1513, 1513a amultistage characteristic curve. Furthermore, the arrangement may besuch that the coil springs in one of the dampers (e.g., the coil springsof the damper 1513) become effective after the coil springs of the otherdamper have already undergone at least some compression, i.e., that oneof the dampers is activated with a preselected delay followingactivation of the other damper in response to angular displacement ofone flywheel relative to the other flywheel and/or vice versa.

The dampers 1513, 1513a can be connected in series and such dampers canbe used in conjunction with one or more inner dampers (not shown). Stillfurther, the apparatus 1501 can comprise three or more dampers at orclose to the same distance from the axes of the flywheels.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of our contributionto the art and, therefore, such adaptations should and are intended tobe comprehended within the meaning and range of equivalence of theappended claims.

We claim:
 1. Apparatus for damping vibrations, comprising at least twoflywheel elements rotatable with and relative to each other about acommon axis and including a first flywheel element connectable with aprime mover and a second flywheel element connectable with atransmission by way of a clutch; and damper means interposed betweensaid flywheel elements and comprising at least two dampers operating inparallel and comprising springs, the springs of one of said at least twodampers being arranged to oppose, alone, a first stage of rotation ofsaid first and second flywheel elements relative to each other from astarting position and the springs of the other of said at least twodampers being arranged to oppose, with the springs of said one damper, anext-following second stage of rotation of said first and secondflywheel elements relative to each other from said starting position,the springs of said one damper having a first end torque and a firsttorsional spring rate and the springs of said other damper having asecond end torque and a second torsional spring rate greater than saidfirst end torque and said first torsional spring rate, the springs ofsaid one damper being disposed at a first radial distance from saidcommon axis and the springs of said other damper being disposed at asecond radial distance from said common axis less than said first radialdistance.
 2. The apparatus of claim 1, wherein said flywheel elementsand said damper means form part of a power train in a motor vehicle,said prime mover constituting an engine and said transmissionconstituting a gearbox of the power train.
 3. The apparatus of claim 1,wherein said clutch includes a friction clutch.
 4. The apparatus ofclaim 1, wherein said springs of said other damper include coil springshaving neighboring convolutions which abut each other in response to apredetermined rotation of said flywheel elements relative to each otherfrom said starting position to thus prevent further rotation of saidflywheel elements relative to each other from said starting position. 5.The apparatus of claim 1, wherein said one damper further comprises afirst input portion and said other damper further comprises a secondinput portion, one of said input portions being rotatable within limitsrelative to the other of said input portions.
 6. The apparatus of claim1, wherein said one damper further comprises an input portion formingpart of said first flywheel element.
 7. The apparatus of claim 1,wherein said dampers further comprise a common input portion affixed tosaid second flywheel element.
 8. The apparatus of claim 1, wherein saidfirst flywheel element includes portions defining at least one annularchamber having a sealed radially outer portion and being at leastpartially filled with a supply of a viscous fluid, at least said onedamper being confined in said at least one chamber.
 9. The apparatus ofclaim 8, wherein said other damper is also confined in said at least onechamber.
 10. The apparatus of claim 8, wherein said dampers furthercomprise an output portion extending radially outwardly away from saidcommon axis and into said at least one chamber.
 11. The apparatus ofclaim 1, wherein said dampers further comprise a common output portionincluding two substantially washer-like members which are connected toeach other and have openings for the springs of said dampers, saidsubstantially washer-like members including spaced-apart portions andsaid openings for the springs of said other damper being provided insaid spaced-apart portions of said substantially washer-like members.12. The apparatus of claim 11, wherein said substantially washer-likemembers further comprise abutting portions provided with pocketsincluding said openings for the springs of said one damper.
 13. Theapparatus of claim 11, wherein said other damper further comprises aninput portion between said spaced-apart portions of said substantiallywasher-like members of said common output portion.
 14. The apparatus ofclaim 11, wherein one of said substantially washer-like members isdirectly connected to said second flywheel element and the other of saidsubstantially washer-like members is affixed to said one substantiallywasher-like member, said one substantially washer-like member having afirst inner diameter and said other substantially washer-like memberhaving a second inner diameter larger than said first inner diameter,said one substantially washer-like member being disposed between saidsecond flywheel element and said other substantially washer-like memberas seen in the direction of said axis.
 15. The apparatus of claim 14,wherein said other damper further comprises an input portion extendingradially toward said common axis beyond said other substantiallywasher-like member.
 16. The apparatus of claim 1, wherein said onedamper further comprises a first input portion and said other damperfurther comprises a second input portion, said input portions beingrotatable relative to each other and said second input portion having aradially inner part provided with at least one stop arranged to limitthe extent of rotation of said input portions relative to each other.17. The apparatus of claim 16, further comprising at least one abutmentfor said at least one stop, said at least one abutment being provided onsaid first flywheel element.
 18. The apparatus of claim 17, wherein saidat least one abutment comprises a rivet affixed to said first flywheelelement, said at least one stop including a projection of said radiallyinner part of said second input portion.
 19. The apparatus of claim 1,wherein said other damper further comprises input and output portions,at least one of said input and output portions having windows snuglyreceiving the springs of said other damper as seen in a circumferentialdirection of said flywheel elements.
 20. The apparatus of claim 1,wherein said first flywheel element includes an annular intermediateportion surrounding an annular chamber of said first flywheel element,said first flywheel element further including two walls extending fromsaid intermediate portion substantially radially inwardly toward saidcommon axis and flanking said annular chamber, said dampers furthercomprising a common output portion disposed between said walls.
 21. Theapparatus of claim 20, wherein one of said walls includes an at leastsubstantially radial flange of said first flywheel element.
 22. Theapparatus of claim 20, wherein one of said walls is disposed between theother of said walls and said second flywheel element as seen in thedirection of said common axis.
 23. The apparatus of claim 20, whereinsaid intermediate portion of said first flywheel element includes anannular extension of one of said walls.
 24. The apparatus of claim 23,wherein the other of said walls comprises a washer affixed to saidintermediate portion and extending substantially radially inwardlytoward said common axis.
 25. The apparatus of claim 1, wherein saidfirst flywheel element includes two sections defining an annular chamberfor at least one of said dampers.
 26. The apparatus of claim 25, whereinsaid sections consist of sheet metal.
 27. The apparatus of claim 1,wherein said first flywheel element defines an annular chamber at leastfor the springs of said one damper and includes two walls flanking saidchamber, said walls having pockets extending in the direction of saidaxis and receiving portions of the springs of said one damper, saidpockets having portions snugly receiving portions of springs of said onedamper.
 28. The apparatus of claim 27, wherein said pockets furtherextend circumferentially of said flywheel elements and said walls havesurfaces bounding said pockets, said springs of said one damper abuttingsaid surfaces under the action of centrifugal force when said firstflywheel element is rotated about said axis.
 29. The apparatus of claim1, wherein said first flywheel element comprises two walls flanking anannular chamber for the springs of said one damper, said chamber havingan inner portion nearer to and a closed outer portion more distant fromsaid axis, and further comprising means for at least partially sealingthe inner portion of said chamber including a diaphragm spring reactingagainst a washer-like member affixed to said second flywheel element andbearing against one of said walls.
 30. The apparatus of claim 1, whereinsaid first flywheel element includes two walls flanking an annularchamber for the springs of said one damper, said walls having pocketsfor the springs of said one damper, surfaces bounding said pockets, andhardened portions defining said surfaces.
 31. The apparatus of claim 30,wherein said hardened portions of said walls are hardened in accordancewith at least one of the procedures including induction hardening, casehardening, laser beam hardening and flame hardening.
 32. The apparatusof claim 30, wherein said hardened portions include layers of awear-resistant material.
 33. The apparatus of claim 32, wherein saidwear-resistant material is selected from the group consisting of nickel,glass fibers, chromium and molybdenum.
 34. The apparatus of claim 30,wherein said hardened portions include receptacles for the springs ofsaid one damper, said receptacles being received in said pockets. 35.The apparatus of claim 30, wherein said pockets form part ofcircumferentially complete annular recesses provided in said walls andsaid one damper further comprises abutments provided in said recessesbetween the springs of said one damper.
 36. The apparatus of claim 35,wherein said abutments include rivets.
 37. The apparatus of claim 35,wherein said abutments have plane surfaces abutting the springs of saidone damper.
 38. The apparatus of claim 35, wherein said abutments haveflattened surfaces abutting the springs of said one damper.
 39. Theapparatus of claim 1, wherein said dampers comprise a common outputportion and said other damper includes an input portion which iscentered by said output portion.
 40. The apparatus of claim 1, whereinsaid first flywheel element has an annular chamber for the springs of atleast one of said dampers and includes two walls flanking said chamberand a sheet metal cage including an annular portion surrounding saidwalls and lateral portions flanking said walls and extending from saidannular portion toward said axis.
 41. The apparatus of claim 1, whereineach spring of said one damper extends circumferentially of saidflywheel elements along an arc of at least 45 degrees.
 42. The apparatusof claim 1, wherein each of said arcs is at least 110 degrees.
 43. Theapparatus of claim 1, wherein said one damper comprises fewer than fivesprings.
 44. The apparatus of claim 43, wherein said one dampercomprises three springs.
 45. The apparatus of claim 1, wherein saiddampers further comprise a common output portion including twosubstantially washer-like members and said other damper furthercomprises an input portion between said substantially washer-likemembers of said common output portion as seen in the direction of saidaxis.
 46. The apparatus of claim 45, wherein said input portion isresiliently deformable in the direction of said axis.
 47. The apparatusof claim 45, wherein said input portion of said other damper includes adiaphragm spring.
 48. The apparatus of claim 45, further comprisingfriction generating insert means between said input portion and at leastone substantially washer-like member of said common output portion. 49.The apparatus of claim 45, further comprising friction reducing insertmeans between said input portion and at least one substantiallywasher-like member of said common output portion.
 50. The apparatus ofclaim 1, wherein said first flywheel element includes portions definingan annular chamber for a portion at least of said damper means, saidportions of said first flywheel element including a lateral wallconstituted by a flange extending substantially radially of said axis.51. The apparatus of claim 50, wherein said portions of said firstflywheel element further include a second wall disposed between saidlateral wall and said second flywheel element.
 52. The apparatus ofclaim 51, wherein said portions of said first flywheel element furtherinclude an annular intermediate portion surrounding said chamber betweensaid walls.
 53. The apparatus of claim 52, wherein at least some of saidsprings bear against said intermediate portion of sad first flywheelelement under the action of centrifugal force in response to rotation ofsaid first flywheel element.
 54. The apparatus of claim 50, wherein saidportions of said first flywheel element include at least onewear-resistant insert which is engaged by at least some of said springsunder the action of centrifugal force in response to rotation of saidfirst flywheel element.
 55. The apparatus of claim 50, wherein saidportions of said first flywheel element further include a second walldisposed between said lateral wall and said second flywheel element, atleast one of said walls consisting of a metallic sheet material.
 56. Theapparatus of claim 55, wherein said at least one wall is said lateralwall.
 57. The apparatus of claim 55, wherein said at least one wall issaid second wall.
 58. The apparatus of claim 1, wherein said firstflywheel element defines an annular chamber for at least some of saidsprings and said damper means further comprises a member non-rotatablyaffixed to said second flywheel element and including projectionsextending into said chamber substantially radially of said axis intoengagement with the springs in said chamber.
 59. The apparatus of claim1, further comprising a frictional damping device in parallel with thesprings of said dampers and arranged to furnish a damping action whichis variable as a function of rotation of said flywheel elements relativeto each other.
 60. The apparatus of claim 5, wherein said damping deviceis constructed and assembled to furnish a damping action which increasesin response to increasing extent of rotation of said first and secondflywheel elements relative to each other from said starting position.61. The apparatus of claim 1, wherein said rotation of said first andsecond flywheel elements relative to each other includes a stage whichprecedes said first stage and during which said rotation is not opposedby the springs of said dampers.
 62. Apparatus for damping vibrations,comprising at least two flywheel elements rotatable with and relative toeach other about a common axis and including a first flywheel elementconnectable with a prime mover and a second flywheel element connectablewith a transmission by way of a clutch; and damper means interposedbetween said flywheel elements and comprising at least two dampersoperating in parallel and comprising springs, the springs of one of saidat least two dampers being arranged to oppose, alone, a first stage ofrotation of said first and second flywheel elements relative to eachother from a starting position and the springs of the other of said atleast two dampers being arranged to oppose, with the springs of said onedamper, a next-following stage of rotation of said first and secondflywheel elements relative to each other from said starting position,said rotation of said flywheel elements relative to each other includinga last stage and said damper means further comprising a frictiongenerating device cooperating with the springs of said other damper tooppose said rotation during said last stage, said friction generatingdevice being arranged to generate a pronounced frictional hysteresis,said springs of said one damper being disposed at a first radialdistance from said axis and said springs of said other damper as well assaid friction generating device being located at a lesser second radialdistance from said axis, said springs of said other damper and saidfrictional hysteresis jointly providing a shock absorber with a highlypronounced end torque.
 63. Apparatus for damping vibrations in a powertrain of a motor vehicle, comprising at least two flywheel elementsrotatable with and relative to each other about a common axis andincluding a first flywheel element connectable with an engine of thepower train and a second flywheel element connectable with atransmission of the power train by way of a clutch; and damper meansinterposed between said flywheel elements and including two dampersoperating in parallel and comprising springs, the springs of one of saidat least two dampers being arranged to oppose, alone, a first stage ofrotation of said first and second flywheel elements relative to eachother from a starting position and the springs of the other of said atleast two dampers being arranged to oppose, with the springs of said onedamper, a next-following stage of rotation of said first and secondflywheel elements relative to each other from said starting position,said springs of said one damper being located at a first radial distancefrom said axis and said springs of said other damper being located at alesser second radial distance from said axis, said springs of said onedamper having a first spring gradient and said springs of said otherdamper having a higher second spring gradient to thus establish apronounced end torque which ensures that pronounced alternating torquesand torque peaks which tend to develop during starting, during stoppageand during operation of the engine at a critical RPM as well as duringthe development of resonance are taken up by said other damper to thusavoid damage to component parts of the motor vehicle.
 64. Apparatus fordamping vibrations, comprising at least two flywheel elements rotatablewith and relative to each other about a common axis and including afirst flywheel element connectable with a prime mover and a secondflywheel element connectable with a transmission by way of a clutch; anddamper means interposed between said first and second flywheel elementsand comprising at least two dampers operating in parallel and comprisingresilient elements, the resilient elements of one of said at least twodampers being arranged to oppose, alone, a first stage of rotation ofsaid first and second flywheel elements relative tb each other from astarting position and the resilient elements of the other of said atleast two dampers being arranged to oppose, with the resilient elementsof said one damper, a next-following stage of rotation of said first andsecond flywheel elements relative to each other from said startingposition, the resilient elements of said one damper being located at afirst radial distance from said axis and the resilient elements of saidother damper being located at a lesser second radial distance from saidaxis, said damper means further comprising a frictional damping deviceoperating in parallel with the resilient elements of said dampers toprovide a damping action which varies as a function of rotation of saidflywheel elements relative to each other.